Installation

First, you need to get the package. Install it with pip:

pip install flask-debugtoolbar-lineprofilerpanel

Somewhere after you’ve set app.debug = True and before app.run, you need to specify the flask_debugtoolbar panels that you want to use and include 'flask_debugtoolbar_lineprofilerpanel.panels.LineProfilerPanel' in that list.

For example, here’s a small flask app with the panel installed and with line profiling enabled for the hello_world:

from flask import Flask
app = Flask(__name__)

import flask_debugtoolbar

from flask_debugtoolbar_lineprofilerpanel.profile import line_profile

@app.route('/')
@line_profile
def hello_world():
    return flask.render_template('hello_world.html')

if __name__ == '__main__':
    app.debug = True

    # Specify the debug panels you want
    app.config['DEBUG_TB_PANELS'] = [
        'flask_debugtoolbar.panels.versions.VersionDebugPanel',
        'flask_debugtoolbar.panels.timer.TimerDebugPanel',
        'flask_debugtoolbar.panels.headers.HeaderDebugPanel',
        'flask_debugtoolbar.panels.request_vars.RequestVarsDebugPanel',
        'flask_debugtoolbar.panels.template.TemplateDebugPanel',
        'flask_debugtoolbar.panels.sqlalchemy.SQLAlchemyDebugPanel',
        'flask_debugtoolbar.panels.logger.LoggingPanel',
        'flask_debugtoolbar.panels.profiler.ProfilerDebugPanel',
        # Add the line profiling
        'flask_debugtoolbar_lineprofilerpanel.panels.LineProfilerPanel'
    ]
    toolbar = flask_debugtoolbar.DebugToolbarExtension(app)

    app.run()

Usage

Unlike the regular profile panel that comes with flask_debugtoolbar, the line profiler will only profile functions you specifically tell it to. You can either use it as a decorator or directly as a function.

from flask_debugtoolbar_lineprofilerpanel.profile import line_profile

# Using it as a decorator
@app.route('/profile')
@line_profile
def profile_page():
    ...
    return flask.render_template('profile_page')

# Explicit argument
line_profile(some_function)

Note that if I had done line_profile(profile_page) in the example above, it would’ve profiled the wrapper created by app.route. In general, you probably just want to use line_profile as a decorator.

Also note that the following will profile the decorator wrapper, not the inner function.

# Using it incorrectly as a decorator
@line_profile
@app.route('/profile')
def profile_page():
    ...
    return flask.render_template('profile_page')

Always use @line_profile as the inner-most decorator.

Using line_profiler with the Google AppEngine SDK

line_profiler is implemented as a C extension. Unfortunately, AppEngine does not support C extensions in the cloud, and dev_appserver simulates this restriction on your local machine. If you’d like to use line_profiler on your local machine, you can monkey-patch the AppEngine SDK to permit it. The Flask-DebugToolbar will make sure this plugin is disabled in production (it will catch any ImportErrors and disable the affected panel).

Simply open application/__init__.py, which should look something like this:

from __future__ import absolute_import

from flask import Flask

app = Flask('application')
app.config.from_object('application.settings')

if app.config['DEBUG']:
    from werkzeug.debug import DebuggedApplication

    app.wsgi_app = DebuggedApplication(app.wsgi_app, evalex=True)


    from flask.ext.debugtoolbar import DebugToolbarExtension

    toolbar = DebugToolbarExtension(app)


import application.urls

and insert the monkey-patch, like so:

from __future__ import absolute_import

from flask import Flask

app = Flask('application')
app.config.from_object('application.settings')

if app.config['DEBUG']:
    from werkzeug.debug import DebuggedApplication

    app.wsgi_app = DebuggedApplication(app.wsgi_app, evalex=True)


    # We can't use LineProfiler in production because it requires a C-extension,
    # but we can monkey-patch it in here for use on the dev server:
    try:
        import os, sys, re

        if 'SERVER_SOFTWARE' in os.environ and os.environ['SERVER_SOFTWARE'].startswith('Dev'):
            # white-list the line_profiler C extension
            sys.meta_path[3]._enabled_regexes.append(re.compile(r'.*line_profiler.*'))

            from flask_debugtoolbar_lineprofilerpanel.profile import line_profile


            ## import the methods you want to profile here, and whitelist them with line_profile:
            #from application.views import YourViewClass
            #
            #line_profile(YourViewClass.the_method_you_want_to_profile)
            #line_profile(YourViewClass.another_method_you_want_to_profile)
    except:
        pass


    # Make sure the monkey-patch is applied before you instantiate the DebugToolbarExtension.
    from flask.ext.debugtoolbar import DebugToolbarExtension

    toolbar = DebugToolbarExtension(app)


import application.urls