Using from __future__ import in Mako template

Question

I have

<%!
    from __future__ import division
%>

at the very top of my template file. I get the error:

SyntaxError: from __future__ imports must occur at the beginning of the file 

What's the correct way to do this?

Answer 1

You cannot use from __future__ import statements in Mako templates. At all.

This is because a Mako template is compiled to a python file, and in order for this to work it sets up some initial structures at the top of that python file:

# -*- encoding:ascii -*-
from mako import runtime, filters, cache
UNDEFINED = runtime.UNDEFINED
__M_dict_builtin = dict
__M_locals_builtin = locals
_magic_number = 7
_modified_time = 1348257499.1626351
_template_filename = '/tmp/mako.txt'
_template_uri = '/tmp/mako.txt'
_source_encoding = 'ascii'
_exports = []

Only after this initial setup is any code from the template itself included. Your from __future__ import division will never be placed first.

You can still use floating point division by casting either operand of the / division operator to a float:

>>> 1 / 2
0
>>> float(1) / 2
0.5

As long as you follow that workaround you can do fine without the division future import.