2018-02-27T18:13:23Z

The Flask Mega-Tutorial Part XIII: I18n and L10n

This is the thirteenth installment of the Flask Mega-Tutorial series, in which I'm going to tell you how to expand Microblog to support multiple languages. As part of that effort you will also learn about creating your own CLI extensions to the flask command.

For your reference, below is a list of the articles in this series.

Note 1: If you are looking for the legacy version of this tutorial, it's here.

Note 2: If you would like to support my work on this blog, or just don't have patience to wait for weekly articles, I am offering the complete version of this tutorial packaged as an ebook or a set of videos. For more information, visit courses.miguelgrinberg.com.

The topics of this chapter are Internationalization and Localization, commonly abbreviated I18n and L10n. To make my application friendly to people who do not speak English, I'm going to implement a translation workflow that, with the help of language translators, will allow me to offer the application to users in a choice of languages.

The GitHub links for this chapter are: Browse, Zip, Diff.

Introduction to Flask-Babel

As you can probably guess, there is a Flask extension that makes working with translations very easy. The extension is called Flask-Babel and is installed with pip:

(venv) $ pip install flask-babel

Flask-Babel is initialized like most other Flask extensions:

app/__init__.py: Flask-Babel instance.

# ...
from flask_babel import Babel

app = Flask(__name__)
# ...
babel = Babel(app)

As part of this chapter, I'm going to show you how to translate the application into Spanish, as I happen to speak that language. I could also work with translators that know other languages and support those as well. To keep track of the list of supported languages, I'm going to add a configuration variable:

config.py: Supported languages list.

class Config(object):
    # ...
    LANGUAGES = ['en', 'es']

I'm using two-letter language codes for this application, but if you need to be more specific, a country code can be added as well. For example, you could use en-US, en-GB and en-CA to support American, British and Canadian English as different languages.

The Babel instance provides a localeselector decorator. The decorated function is invoked for each request to select a language translation to use for that request:

app/__init__.py: Select best language.

from flask import request

# ...

@babel.localeselector
def get_locale():
    return request.accept_languages.best_match(app.config['LANGUAGES'])

Here I'm using an attribute of Flask's request object called accept_languages. This object provides a high-level interface to work with the Accept-Language header that clients send with a request. This header specifies the client language and locale preferences as a weighted list. The contents of this header can be configured in the browser's preferences page, with the default being usually imported from the language settings in the computer's operating system. Most people don't even know such a setting exists, but this is useful as users can provide a list of preferred languages, each with a weight. In case you are curious, here is an example of a complex Accept-Languages header:

Accept-Language: da, en-gb;q=0.8, en;q=0.7

This says that Danish (da) is the preferred language (with default weight = 1.0), followed by British English (en-GB) with a 0.8 weight, and as a last option generic English (en) with a 0.7 weight.

To select the best language, you need to compare the list of languages requested by the client against the languages the application supports, and using the client provided weights, find the best language. The logic to do this is somewhat complicated, but it is all encapsulated in the best_match() method, which takes the list of languages offered by the application as an argument and returns the best choice.

Marking Texts to Translate In Python Source Code

Okay, so now comes the bad news. The normal workflow when making an application available in multiple languages is to mark all the texts that need translations in the source code. After the texts are marked, Flask-Babel will scan all the files and extract those texts into a separate translation file using the gettext tool. Unfortunately this is a tedious task that needs to be done to enable translations.

I'm going to show you a few examples of this marking here, but you can get the complete set of changes from the download package for this chapter or the GitHub repository.

The way texts are marked for translation is by wrapping them in a function call that as a convention is called _(), just an underscore. The simplest cases are those where literal strings appear in the source code. Here is an example flash() statement:

from flask_babel import _
# ...
flash(_('Your post is now live!'))

The idea is that the _() function wraps the text in the base language (English in this case). This function will use the best language selected by the function decorated with the localeselector function to find the correct translation for a given client. The _() function then returns the translated text, which in this case will become the argument to flash().

Unfortunately not all cases are that simple. Consider this other flash() call from the application:

flash('User {} not found.'.format(username))

This text has a dynamic component that is inserted in the middle of the static text. The _() function has a syntax that supports this type of texts, but it is based on the older string substitution syntax:

flash(_('User %(username)s not found.', username=username))

There is an even harder case to handle. Some string literals are assigned outside of a request, usually when the application is starting up, so at the time these texts are evaluated there is no way to know what language to use. An example of this is the labels associated with form fields. The only solution to handle those texts is to find a way to delay the evaluation of the string until it is used, which is going to be under an actual request. Flask-Babel provides a lazy evaluation version of _() that is called lazy_gettext():

from flask_babel import lazy_gettext as _l

class LoginForm(FlaskForm):
    username = StringField(_l('Username'), validators=[DataRequired()])
    # ...

Here I'm importing this alternative translation function and renaming to to _l() so that it looks similar to the original _(). This new function wraps the text in a special object that triggers the translation to be performed later, when the string is used.

The Flask-Login extension flashes a message any time it redirects the user to the login page. This message is in English and comes from the extension itself. To make sure this message also gets translated, I'm going to override the default message and provide my own, wrapper with the _l() function for lazy processing:

login = LoginManager(app)
login.login_view = 'login'
login.login_message = _l('Please log in to access this page.')

Marking Texts to Translate In Templates

In the previous section you've seen how to mark translatable texts in Python source code, but that is only a part of this process, as template files also have text. The _() function is also available in templates, so the process is fairly similar. For example, consider this snippet of HTML from 404.html:

<h1>File Not Found</h1>

The translation enabled version becomes:

<h1>{{ _('File Not Found') }}</h1>

Note that here in addition to wrapping the text with _(), the {{ ... }} needs to be added, to force the _() to be evaluated instead of being considered a literal in the template.

For more complex phrases that have dynamic components, arguments can also be used:

<h1>{{ _('Hi, %(username)s!', username=current_user.username) }}</h1>

There is a particularly tricky case in _post.html that took me a while to figure out:

        {% set user_link %}
            <a href="{{ url_for('user', username=post.author.username) }}">
                {{ post.author.username }}
            </a>
        {% endset %}
        {{ _('%(username)s said %(when)s',
            username=user_link, when=moment(post.timestamp).fromNow()) }}

The problem here is that I wanted the username to be a link that points to the profile page of the user, not just the name, so I had to create an intermediate variable called user_link using the set and endset template directives, and then pass that as an argument to the translation function.

As I mentioned above, you can download a version of the application with all the translatable texts in Python source code and templates marked.

Extracting Text to Translate

Once you have the application with all the _() and _l() in place, you can use the pybabel command to extract them to a .pot file, which stands for portable object template. This is a text file that includes all the texts that were marked as needing translation. The purpose of this file is to serve as a template to create translation files for each language.

The extraction process needs a small configuration file that tells pybabel what files should be scanned for translatable texts. Below you can see the babel.cfg that I created for this application:

babel.cfg: PyBabel configuration file.

[python: app/**.py]
[jinja2: app/templates/**.html]
extensions=jinja2.ext.autoescape,jinja2.ext.with_

The first two lines define the filename patterns for Python and Jinja2 template files respectively. The third line defines two extensions provided by the Jinja2 template engine that help Flask-Babel properly parse template files.

To extract all the texts to the .pot file, you can use the following command:

(venv) $ pybabel extract -F babel.cfg -k _l -o messages.pot .

The pybabel extract command reads the configuration file given in the -F option, then scans all the code and template files in the directories that match the configured sources, starting from the directory given in the command (the current directory or . in this case). By default, pybabel will look for _() as a text marker, but I have also used the lazy version, which I imported as _l(), so I need to tell the tool to look for those too with the -k _l. The -o option provides the name of the output file.

I should note that the messages.pot file is not a file that needs to be incorporated into the project. This is a file that can be easily regenerated any time it is needed, simply by running the command above again. So there is no need to commit this file to source control.

Generating a Language Catalog

The next step in the process is to create a translation for each language that will be supported in addition to the base one, which in this case is English. I said I was going to start by adding Spanish (language code es), so this is the command that does that:

(venv) $ pybabel init -i messages.pot -d app/translations -l es
creating catalog app/translations/es/LC_MESSAGES/messages.po based on messages.pot

The pybabel init command takes the messages.pot file as input and writes a new language catalog to the directory given in the -d option for the language specified in the -l option. I'm going to be installing all the translations in the app/translations directory, because that is where Flask-Babel will expect translation files to be by default. The command will create a es subdirectory inside this directory for the Spanish data files. In particular, there will be a new file named app/translations/es/LC_MESSAGES/messages.po, that is where the translations need to be made.

If you want to support other languages, just repeat the above command with each of the language codes you want, so that each language gets its own repository with a messages.po file.

This messages.po file that created in each language repository uses a format that is the de facto standard for language translations, the format used by the gettext utility. Here are a few lines from the beginning of the Spanish messages.po:

# Spanish translations for PROJECT.
# Copyright (C) 2017 ORGANIZATION
# This file is distributed under the same license as the PROJECT project.
# FIRST AUTHOR <EMAIL@ADDRESS>, 2017.
#
msgid ""
msgstr ""
"Project-Id-Version: PROJECT VERSION\n"
"Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
"POT-Creation-Date: 2017-09-29 23:23-0700\n"
"PO-Revision-Date: 2017-09-29 23:25-0700\n"
"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
"Language: es\n"
"Language-Team: es <LL@li.org>\n"
"Plural-Forms: nplurals=2; plural=(n != 1)\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=utf-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Generated-By: Babel 2.5.1\n"

#: app/email.py:21
msgid "[Microblog] Reset Your Password"
msgstr ""

#: app/forms.py:12 app/forms.py:19 app/forms.py:50
msgid "Username"
msgstr ""

#: app/forms.py:13 app/forms.py:21 app/forms.py:43
msgid "Password"
msgstr ""

If you skip the header, you can see that what follows is a list of strings that were extracted from the _() and _l() calls. For each text, you get a reference to the location of the text in your application. Then the msgid line contains the text in the base language, and the msgstr line that follows contains an empty string. Those empty strings need to be edited to have the version of the text in the target language.

There are many translation applications that work with .po files. If you feel comfortable editing the text file, then that's sufficient, but if you are working with a large project it may be recommended to work with a specialized editor. The most popular translation application is the open-source poedit, which is available for all major operating systems. If you are familiar with vim, then the po.vim plugin gives some key mappings that make working with these files easier.

Below you can see a portion of the Spanish messages.po after I added the translations:

#: app/email.py:21
msgid "[Microblog] Reset Your Password"
msgstr "[Microblog] Nueva Contraseña"

#: app/forms.py:12 app/forms.py:19 app/forms.py:50
msgid "Username"
msgstr "Nombre de usuario"

#: app/forms.py:13 app/forms.py:21 app/forms.py:43
msgid "Password"
msgstr "Contraseña"

The download package for this chapter also contains this file with all the translations in place, so that you don't have to worry about that part for this application.

The messages.po file is a sort of source file for translations. When you want to start using these translated texts, this file needs to be compiled into a format that is efficient to be used by the application at run-time. To compile all the translations for the application, you can use the pybabel compile command as follows:

(venv) $ pybabel compile -d app/translations
compiling catalog app/translations/es/LC_MESSAGES/messages.po to
app/translations/es/LC_MESSAGES/messages.mo

This operation adds a messages.mo file next to messages.po in each language repository. The .mo file is the file that Flask-Babel will use to load translations for the application.

After you create the messages.mo file for Spanish or any other languages you added to the project, these languages are ready to be used in the application. If you want to see how the application looks in Spanish, you can edit the language configuration in your web browser to have Spanish as the preferred language. For Chrome, this is the Advanced part of the Settings page:

Chrome Language Options

If you prefer not to change your browser settings, the other alternative is to force a language by making the localeselector function always return it. For Spanish, this would be how you would do it:

app/__init__.py: Select best language.

@babel.localeselector
def get_locale():
    # return request.accept_languages.best_match(app.config['LANGUAGES'])
    return 'es'

Running the application with the browser configured for Spanish, or the localeselector function returning es will make all the texts appear in Spanish when you use the application.

Updating the Translations

One common situation when working with translations is that you may want to start using a translation file even if it is incomplete. That is totally fine, you can compile an incomplete messages.po file and any translations that are available will be used, while any missing ones will use the base language. You can then continue working on the translations and compile again to update the messages.mo file as you make progress.

Another common scenario occurs if you missed some texts when you added the _() wrappers. In this case you are going to see that those texts that you missed are going to remain in English, because Flask-Babel knows nothing about them. In this situation you'll want to add the _() or _l() wrappers when you detect texts that don't have them, and then do an update procedure, which involves two steps:

(venv) $ pybabel extract -F babel.cfg -k _l -o messages.pot .
(venv) $ pybabel update -i messages.pot -d app/translations

The extract command is identical to the one I issued earlier, but now it will generate a new version of messages.pot with all the previous texts plus anything new that you recently wrapped with _() or _l(). The update call takes the new messages.pot file and merges it into all the messages.po files associated with the project. This is going to be an intelligent merge, in which any existing texts will be left alone, while only entries that were added or removed in messages.pot will be affected.

After the messages.po are updated, you can go ahead and translate any new tests, then compile the messages one more time to make them available to the application.

Translating Dates and Times

Now I have a complete Spanish translation for all the texts in Python code and templates, but if you run the application in Spanish and are a good observer, you will notice that there are still a few things that appear in English. I'm referring to the timestamps generated by Flask-Moment and moment.js, which obviously have not been included in the translation effort because none of the texts generated by these packages are part of the source code or templates of the application.

The moment.js library does support localization and internationalization, so all I need to do is configure the proper language. Flask-Babel returns the selected language and locale for a given request via the get_locale() function, so what I'm going to do is add the locale to the g object, so that I can then access it from the base template:

app/routes.py: Store selected language in flask.g.

# ...
from flask import g
from flask_babel import get_locale

# ...

@app.before_request
def before_request():
    # ...
    g.locale = str(get_locale())

The get_locale() function from Flask-Babel returns a locale object, but I just want to have the language code, which can be obtained by converting the object to a string. Now that I have g.locale, I can access it from the base template to configure moment.js with the correct language:

app/templates/base.html: Set locale for moment.js.

...
{% block scripts %}
    {{ super() }}
    {{ moment.include_moment() }}
    {{ moment.lang(g.locale) }}
{% endblock %}

And now all dates and times should appear in the same language as the text. Below you can see how the application looks in Spanish:

Microblog in Español

At this point, all texts except those that were provided by the user in blog posts or profile descriptions should be translatable into other languages.

Command-Line Enhancements

You will probably agree with me that the pybabel commands are a bit long and difficult to remember. I'm going to use this opportunity to show you how you can create custom commands that are integrated with the flask command. So far, you've seen me use flask run, flask shell, and several flask db sub-commands provided by the Flask-Migrate extension. It is actually easy to add application-specific commands to flask as well. So what I'm going to do now is create a few simple commands that trigger the pybabel commands with all the arguments that are specific to this application. The commands that I'm going to add are:

  • flask translate init LANG to add a new language
  • flask translate update to update all language repositories
  • flask translate compile to compile all language repositories

The babel extract step is not going to be a command, because generating the messages.pot file is always a pre-requisite to running either the init or the update commands, so the implementation of these commands will generate the translation template file as a temporary file.

Flask relies on Click for all its command-line operations. Commands like translate, which are a root for several sub-commands are created via the app.cli.group() decorator. I'm going to put these commands in a new module called app/cli.py:

app/cli.py: Translate command group.

from app import app

@app.cli.group()
def translate():
    """Translation and localization commands."""
    pass

The name of the command comes from the name of the decorated function, and the help message comes from the docstring. Since this is a parent command that only exists to provide a base for the sub-commands, the function itself does not need to do anything.

The update and compile are easy to implement, because they do not take any arguments:

app/cli.py: Update and compile sub-commands.

import os

# ...

@translate.command()
def update():
    """Update all languages."""
    if os.system('pybabel extract -F babel.cfg -k _l -o messages.pot .'):
        raise RuntimeError('extract command failed')
    if os.system('pybabel update -i messages.pot -d app/translations'):
        raise RuntimeError('update command failed')
    os.remove('messages.pot')

@translate.command()
def compile():
    """Compile all languages."""
    if os.system('pybabel compile -d app/translations'):
        raise RuntimeError('compile command failed')

Note how the decorator from these functions is derived from the translate parent function. This may seem confusing, since translate() is a function, but it is the standard way in which Click builds groups of commands. Same as with the translate() function, the docstrings for these functions are used as help message in the --help output.

You can see that for all commands, I run them and make sure that the return value is zero, which implies that the command did not return any error. If the command errors, then I raise a RuntimeError, which will cause the script to stop. The update() function combines the extract and update steps in the same command, and if everything is successful, it deletes the messages.pot file after the update is complete, since this file can be easily regenerated when needed again.

The init command takes the new language code as an argument. Here is the implementation:

app/cli.py: Init sub-command.

import click

@translate.command()
@click.argument('lang')
def init(lang):
    """Initialize a new language."""
    if os.system('pybabel extract -F babel.cfg -k _l -o messages.pot .'):
        raise RuntimeError('extract command failed')
    if os.system(
            'pybabel init -i messages.pot -d app/translations -l ' + lang):
        raise RuntimeError('init command failed')
    os.remove('messages.pot')

This command uses the @click.argument decorator to define the language code. Click passes the value provided in the command to the handler function as an argument, and then I incorporate the argument into the init command.

The final step to enable these commands to work is to import them, so that the commands get registered. I decided to do this in the microblog.py file in the top-level directory:

microblog.py: Register command-line commands.

from app import cli

Here the only thing I need to do is import the new cli.py module, there is no need to do anything with it, as the import causes the command decorators to run and register the command.

At this point, running flask --help will list the translate command as an option. And flask translate --help will show the three sub-commands that I defined:

(venv) $ flask translate --help
Usage: flask translate [OPTIONS] COMMAND [ARGS]...

  Translation and localization commands.

Options:
  --help  Show this message and exit.

Commands:
  compile  Compile all languages.
  init     Initialize a new language.
  update   Update all languages.

So now, the workflow is much simpler and there is no need to remember long and complicated commands. To add a new language, you use:

(venv) $ flask translate init <language-code>

To update all the languages after making changes to the _() and _l() language markers:

(venv) $ flask translate update

And to compile all languages after updating the translation files:

(venv) $ flask translate compile

102 comments

  • #51 Nico said 2018-10-19T20:36:27Z

    Hi Miguel, thank you for the tutorial! I am stuck at extracting the text to translate. I get this: $ pybabel extract -F babel.cfg -k _l -o messages.pot Usage: pybabel extract [options] <input-paths> pybabel: error: no input files or directories specified My config file is exactly like yours. Thank you in advance from Buenos Aires!

  • #52 Miguel Grinberg said 2018-10-20T08:58:21Z

    @Nico: there is a dot at the end of the command that you missed. That tells pybabel which directory to scan for text to translate.

  • #53 Joseph said 2018-11-06T17:29:46Z

    Hello, I keep getting a jinja2 error. the last line reads: File: "File\Path\To\Project\lexer.py", line 384, in expect self.name, self.filename jinja2.exceptions.TemplateSyntaxError: expected token ',', got 'Found' 127.0.0.1 - - [06/Nov/2018 11:19:12] " Get /favicon.ico HTTP/1.1" 500 - Any Ideas on what is causing that?

  • #54 Miguel Grinberg said 2018-11-06T18:14:38Z

    @Joseph: did you look at your template, in the place where the word "Found" appears? The error message indicates you have a problem there, can't tell you what it is because you haven't shown the template.

  • #55 Joseph said 2018-11-07T22:09:33Z

    Hello, I have not, this is something i believe i used pip for. I was following your tutorial to a T. Unless I missed something, I did not see anything other than the babel.cfg file you had us create: [python: app/**.py] [jinja2: app/templates/**.html] extensions=jinja2.ext.autoescape,jinja2.ext.with_ Also, whenever I type in the translate command, even `flask translate --help`, I get a: INFO in__init__: Microblog startup Usage: flask [OPTIONS] COMMAND [ARGS]... Error: No such command "translate". Here is my __init__ file: from flask_babel import Babel, lazy_gettext as _l from config import Config app = Flask(__name__) app.config.from_object(Config) db = SQLAlchemy(app) migrate = Migrate(app, db) login = LoginManager(app) login.login_view = 'login' login.login_message = _l('Please log in to access this page.') mail = Mail(app) bootstrap = Bootstrap(app) moment = Moment(app) babel = Babel(app) if not app.debug: if app.config['MAIL_SERVER']: auth = None if app.config['MAIL_USERNAME'] or app.config['MAIL_PASSWORD']: auth = (app.config['MAIL_USERNAME'], app.config['MAIL_PASSWORD']) secure = None if app.config['MAIL_USE_TLS']: secure = () mail_handler = SMTPHandler( mailhost=(app.config['MAIL_SERVER'], app.config['MAIL_PORT']), fromaddr='no-reply@' + app.config['MAIL_SERVER'], toaddrs=app.config['ADMINS'], subject='Microblog Failure', credentials=auth, secure=secure) mail_handler.setLevel(logging.ERROR) app.logger.addHandler(mail_handler) if not os.path.exists('logs'): os.mkdir('logs') file_handler = RotatingFileHandler('logs/microblog.log', maxBytes=10240, backupCount=10) file_handler.setFormatter(logging.Formatter('%(asctime)s %(levelname)s: %(message)s [in %(pathname)s:%(lineno)d]')) file_handler.setLevel(logging.INFO) app.logger.addHandler(file_handler) app.logger.setLevel(logging.INFO) app.logger.info('Microblog startup') @babel.localeselector def get_locale(): return request.accept_languages.best_match(app.config['LANGUAGES']) from app import routes, models, errors

  • #56 Miguel Grinberg said 2018-11-07T22:42:37Z

    @Joseph: you may need to download the code from this chapter and compare it against yours. You are missing steps.

  • #57 Norman Dantzig said 2018-11-15T06:03:12Z

    Hi Miguel, If I skip this section will it affect my ability to do later sections?

  • #58 Miguel Grinberg said 2018-11-15T12:03:26Z

    @Norman: it will not affect your learning of other topics, but translations are used in some of the remaining chapters too.

  • #59 Ankur Jyoti Phukan said 2018-12-01T11:59:07Z

    Hello Miguel, Thank you for writing such a nice tutorial, I am not able to pin point the error reason can you help me. Traceback (most recent call last): File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 2375, in __call__ return self.wsgi_app(environ, start_response) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 2361, in wsgi_app response = self.handle_exception(e) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 1797, in handle_exception reraise(exc_type, exc_value, tb) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise raise value File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 2358, in wsgi_app response = self.full_dispatch_request() File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 1875, in full_dispatch_request rv = self.handle_user_exception(e) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 1774, in handle_user_exception reraise(exc_type, exc_value, tb) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise raise value File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 1873, in full_dispatch_request rv = self.dispatch_request() File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 1859, in dispatch_request return self.view_functions[rule.endpoint](**req.view_args) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask_login/utils.py", line 271, in decorated_view return func(*args, **kwargs) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/app/routes.py", line 38, in index return render_template('index.html', title=_('Home'), form=form, posts=posts.items, next_url=next_url,prev_url=prev_url) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/templating.py", line 137, in render_template ctx.app, File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask/templating.py", line 117, in _render rv = template.render(context) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/jinja2/asyncsupport.py", line 81, in render return original_render(self, *args, **kwargs) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/jinja2/environment.py", line 1096, in render return self.environment.handle_exception(exc_info, True) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/jinja2/environment.py", line 850, in handle_exception reraise(exc_type, exc_value, tb) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/jinja2/_compat.py", line 38, in reraise raise value.with_traceback(tb) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/app/templates/index.html", line 2, in top-level template code {% import 'bootstrap/wtf.html' as wtf %} File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/app/templates/base.html", line 1, in top-level template code {% extends 'bootstrap/base.html' %} File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask_bootstrap/templates/bootstrap/base.html", line 1, in top-level template code {% block doc -%} File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask_bootstrap/templates/bootstrap/base.html", line 4, in block "doc" {%- block html %} File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask_bootstrap/templates/bootstrap/base.html", line 20, in block "html" {% block body -%} File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/flask_bootstrap/templates/bootstrap/base.html", line 23, in block "body" {% block content -%} File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/app/templates/base.html", line 48, in block "content" {% block app_content %}{% endblock %} File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/app/templates/index.html", line 5, in block "app_content" <h1>{{ _('Hi, %(username)s!', username=current_user.username) }}</h1> File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/jinja2/ext.py", line 150, in _gettext_alias return __context.call(__context.resolve("gettext"), *args, **kwargs) File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/jinja2/ext.py", line 159, in gettext return rv % variables File "/media/leo/softwaerAndTutorial/Programming/python/webProject/microblog/venv/lib/python3.6/site-packages/markupsafe/__init__.py", line 102, in __mod__ return self.__class__(text_type.__mod__(self, arg)) ValueError: unsupported format character '!' (0x21) at index 16

  • #60 Miguel Grinberg said 2018-12-02T08:59:54Z

    @Ankur: Hmm. Does it work if you remove the exclamation mark in the greeting on file index.html?

  • #61 Bruno said 2019-01-06T03:28:14Z

    One other doubt, In case I wanted to use en-US, en-CA, pt-BR, pt-PT how should I set it in the LANGUAGES (in config.py) so that babel recognize them proper (it seems babel do not accept '-' symbol char)

  • #62 Miguel Grinberg said 2019-01-06T08:40:04Z

    @Bruno: Have you tried an underscore instead of a dash? en_US, en_CA and so on?

  • #63 Markus said 2019-01-06T22:13:49Z

    @Miguel Grinberg: I have the same problem like Sujay. I'm using Pycharm. FLASK_APP seems ok. From the official Flask tutorial I was knowing that I must register the cli commands. The code comes unchanged from your repository of Github. After adding this code inside cli.py: def init_app(app): app.cli.add_command(init) app.cli.add_command(update) app.cli.add_command(compile) and this inside app/__init__.py from app.cli import init_app init_app(app) I see the comands. It's not really perfect because the cli subcommand are working: (venv) C:\Users\Markus\PycharmProjects\microblog>flask translate --help [2019-01-06 23:11:19,174] INFO in __init__: Microblog startup Usage: flask translate [OPTIONS] COMMAND [ARGS]... Translation and localization commands. Options: --help Show this message and exit. Commands: compile Compile all languages. init Initialize a new language. update Update all languages. Further I found out that with flask --help the commands are shown: Commands: compile Compile all languages. db Perform database migrations. init Initialize a new language. routes Show the routes for the app. run Runs a development server. shell Runs a shell in the app context. translate Translation and localization commands. update Update all languages. Any idea? Seems to be a Pycharm venv problem maybe? Thanks, Markus

  • #64 Miguel Grinberg said 2019-01-07T10:41:51Z

    @Markus: the code as explained in this tutorial should work just fine, there is no need to make any changes to what I've done, all the commands are properly registered in my version. The problem with PyCharm might be that the FLASK_APP environment variable is not defined correctly. One trick you can use is to open a terminal, do the "export FLASK_APP=microblog.py" or "set FLASK_APP=microblog.py" depending on your OS, and then start pycharm from that terminal session, so that the variable is defined in the context of the PyCharm process and all its sub-processes. Another approach is to install python-dotenv and then write the FLASK_APP variable into the .flaskenv file, as shown in Chapter 1 of this tutorial.

  • #65 How can I add my native language, Laos language said 2019-01-21T10:00:48Z

    Thank for Great Tutorial But I want to add Laos Language, How can I add my native language

  • #66 Miguel Grinberg said 2019-01-22T10:20:11Z

    You do it in the same way as I've done the Spanish language. The steps are exactly the same.

  • #67 Aleksander said 2019-01-30T14:10:38Z

    The auto translation is nice, but if for some reason you find yourself using a computer abroad with a different language setting than what you are using this could be somewhat of a challenge. how to you implement a language selection for a user to override the automatic one?

  • #68 Miguel Grinberg said 2019-01-30T15:15:51Z

    @Aleksander: to select a language explicitly the logic in the get_locale() function needs to change to return the chosen language for each user. It can get the language from a cookie, or from a setting stored in the database for each user, depending on how you want the user to make a language selection.

  • #69 Tobias said 2019-02-01T16:57:49Z

    Very nice tutorial, just awesome! I want to give something back just a little :) import os.path as op import glob as gl @translate.command() @click.argument('lang') def remove(lang: str): """Remove language from translations. :param lang: Language identifier after ISO639 e.g. 'de' for german or 'nl' for dutch. :type lang: str. :raises: RunTimeError. """ path = 'app/translations/' + lang if not os.path.isdir(path): raise RuntimeError("remove command failed") [os.remove(f) for f in gl.glob(op.join(path, '**'), recursive=True) if op.isfile(f)] [os.removedirs(d) for d in gl.glob(op.join(path, '**'), recursive=True)[::-1] if op.isdir(d)]

  • #70 taewoo said 2019-03-13T07:35:30Z

    __init__.py . . from flask_babel import Babel from flask_babel import lazy_gettext as _l @babel.localeselector def get_locale(): print(request.accept_languages.best_match(app.config['LANGUAGES'])) return request.accept_languages.best_match(app.config['LANGUAGES']) -------------------------------------------------------------------------- config.py class Config(object): SECRET_KEY = os.environ.get('SECRET_KEY') or 'you-will-never-guess' SQLALCHEMY_DATABASE_URI = 'sqlite:///' + os.path.join(basedir, 'app.db') SQLALCHEMY_TRACK_MODIFICATIONS = False POSTS_PER_PAGE = 3 LANGUAGES = ['en', 'ko'] ------------------------- base.html ... {% with messages = get_flashed_messages() %} {% if messages %} {% for message in messages %} <div class="alert alert-info" role="alert">{{ message }}</div> {% endfor %} {% endif %} {% endwith %} .... -------------------------------------------------------------- route.py from flask_babel import _ @app.route('/index', methods=['GET', 'POST']) ... flash(_('hi')) .... -------------------------------------------------------------- in base.html 'hi' is not Translation. just view 'hi'. request.accept_languages.best_match(app.config['LANGUAGES']) is return ko helpme

  • #71 Miguel Grinberg said 2019-03-13T09:35:24Z

    @taewoo: did you create a translation dictionary for your language as shown in this article?

  • #72 Chris said 2019-04-25T20:02:17Z

    Hi Miguel. Great tutorial series. I'm really enjoying it. Thank you. I'm also getting the dreaded: Error: No such command "translate". I have exactly the same cli.py and microblog.py as you (I overwrote mine with yours) and have the FLASK_APP variable set. 'flask run' works fine. Is there anything else that I could have missed that would explain why it's not working? Another question I have is about the line: 'from app import app' in cli.py. What is this line actually doing? I'm struggling to understand it's purpose. Thanks again. Chris

  • #73 Miguel Grinberg said 2019-04-26T07:17:40Z

    @Chris: what did you set FLASK_APP to? What is the output that you see in your console when you run "flask run"?

  • #74 Chris said 2019-05-02T09:05:08Z

    I have FLASK_APP set to microblog.py 'flask run' gives me the usual: * Environment: production WARNING: Do not use the development server in a production environment. Use a production WSGI server instead. * Debug mode: off * Running on http://0.0.0.0:3000/ (Press CTRL+C to quit) Thanks. Chris

  • #75 Miguel Grinberg said 2019-05-02T20:18:16Z

    @Chris: you are actually adding arguments to "flask run", right? What is the exact command that you are running? Also, if you are doing this on Mac or Linux, are you sure you exported FLASK_APP? If you set the variable but don't export it, then child processes do not inherit the variable. Regarding your other question, when you do "from app import app" the first "app' refers to the app package, while the second "app" refers to a variable named app. We are importing the "app" variable from the "app" package. Some people find it more clear to rename the package to something else such as "myapp". Then the command becomes "from myapp import app".

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