Install

Flask-CSV is packaged and you can use pip to install it:

pip install flask_csv

How to use ?

Flask-CSV has a simple hepler method named send_csv which allows you to send csv files in flask endpoints. It takes an iterable of dict, a filename and a list of fields. The keys of all dict in the iterable must correspond to given fields.

It will return a Response object with filename set and body containing the CSV data.

You will better understand with a short example.

@app.route("/")
def index():
    return send_csv([{"id": 42, "foo": "bar"}, {"id": 91, "foo": "baz"}],
                    "test.csv", ["id", "foo"])

Hitting this endpoint will return:

id,foo
42,bar
91,baz

Passing additionnal parameters

The remaining arguments of send_csv will be passed to send_file. For example, to disable caching, do the following:

send_csv([{"id": 42, "foo": "bar"}, {"id": 91, "foo": "baz"}],
         "test.csv", ["id", "foo"], cache_timeout=0)

You can also pass additionnal parameters to the CSV writer like this:

send_csv([{"foo": 42}, {"bar": "baz"}], "test.csv", ["foo"],
         writer_kwargs={"extrasaction": "ignore"})

In this example, the “bar” key will not raise a ValueError since the writer will be given the parameter extrasaction with the value “ignore”.

Change delimiter

You can also change the delimiter with the delimiter option.

send_csv([{"id": 42, "foo": "bar"}, {"id": 91, "foo": "baz"}],
         "test.csv", ["id", "foo"], delimiter=';')

Will result in:

id;foo
42;bar
91;baz

Specifying file encoding

You can also specify the encoding used to send the file, with the encoding option (utf-8 by default).

send_csv([{"id": 42, "foo": "bar"}, {"id": 91, "foo": "baz"}],
         "test.csv", ["id", "foo"], encoding='iso-8859-1')

Use Marshmallow Schemas

You can use Schema from marshmallow by passing it as schema to send_csv. If you want to keep only ids and ensure they are integers, you could do:

class IdSchema(Schema):
    id = fields.Integer()

send_csv([{"id": 42, "foo": "bar"}, {"id": 91, "foo": "baz"}],
         "test.csv", ["id", "foo"], schema=IdSchema())

And that would result in this:

id
42
91

SystemError returned a result with an error set

When using uwsgi for your flask app, it might raise this kind of error on the send_file method. If that were the case, adding the following option to your uwsgi conf should solve it :

wsgi-disable-file-wrapper = true