Jinja2 and Flask: Pass variable into parent template without passing it into children

May I suggest you use the global variable 'g' in flask. This is by default available in the jinja templates. So you don't need to worry about passing it anywhere in the base template or children. Just make sure you set it first when you login

g.username = user.name

then in templates, just do this:

You are logged in as {{ g.username }}

You need to use Flask's context-processors:

@app.context_processordef inject_user():    return dict(user=g.user)

See this similar SO question and answer.

An example of how I am using it (to simply insert app config settings):

@app.context_processordef lib_versions():    return dict(        bokehversion = app.config['BOKEH_VERSION'],        jqueryversion = app.config['JQUERY_VERSION'],        jqueryuiversion = app.config['JQUERYUI_VERSION'],        bootstrapversion = app.config['BOOTSTRAP_VERSION'],    )

Which are pulled from my Flask config file:

class Config(object):    DEBUG = True    TESTING = True    SQLALCHEMY_DATABASE_URI = ''    TMP_DIR = ''    STATIC_FOLDER = ''    BOKEH_VERSION = '0.8.2'    JQUERY_VERSION = '1.11.2'    JQUERYUI_VERSION = '1.11.4'    BOOTSTRAP_VERSION = '3.3.4'class ProductionConfig(Config):    DEBUG = False    TESTING = False

You then call these in your base template just like any other Jinja2 variable:

<!-- START: CSS --><link rel="stylesheet" media="screen" type="text/css" href="http://cdn.bokeh.org/bokeh/release/bokeh-{{ bokehversion }}.min.css"><!-- END: CSS --><!-- START: JS --><script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/{{ jqueryversion }}/jquery.min.js"></script><script src="http://ajax.googleapis.com/ajax/libs/jqueryui/{{ jqueryuiversion }}/jquery-ui.min.js"></script><script type="text/javascript" src="//maxcdn.bootstrapcdn.com/bootstrap/{{ bootstrapversion }}/js/bootstrap.min.js"></script><!-- END: JS -->