Cannot use the variable name "inf" in templates

[Fraser Nevett]

Trying to render a template variable named inf does not work:

>>> from django.template import Template, Context
>>> Template('{{ inf }}').render(Context({'inf': 'xxx'}))
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/tmp/venv/lib/python2.7/site-packages/django/template/base.py", line 191, in __init__
    self.nodelist = self.compile_nodelist()
  File "/tmp/venv/lib/python2.7/site-packages/django/template/base.py", line 233, in compile_nodelist
    e.template_debug = self.get_exception_info(e, e.token)
AttributeError: 'exceptions.OverflowError' object has no attribute 'token'

It also fails if the variable is undefined in the context:

>>> Template('{{ inf }}').render(Context())
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/tmp/venv/lib/python2.7/site-packages/django/template/base.py", line 191, in __init__
    self.nodelist = self.compile_nodelist()
  File "/tmp/venv/lib/python2.7/site-packages/django/template/base.py", line 233, in compile_nodelist
    e.template_debug = self.get_exception_info(e, e.token)
AttributeError: 'exceptions.OverflowError' object has no attribute 'token'

This is happening because 'inf' is used in Python to represent infinity:

>>> float('inf')
inf

The problem appears to be with ​this bit of the code:

            # First try to treat this variable as a number.
            #
            # Note that this could cause an OverflowError here that we're not
            # catching. Since this should only happen at compile time, that's
            # probably OK.
            self.literal = float(var)

            # So it's a float... is it an int? If the original value contained a
            # dot or an "e" then it was a float, not an int.
            if '.' not in var and 'e' not in var.lower():
                self.literal = int(self.literal)

It successfully converts the string 'inf' to a float with value of infinity, but then trying to convert this float to an int causes the OverflowError:

>>> int(float('inf'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: cannot convert float infinity to integer

Python also supports floats of '-inf' and 'nan'. Using '-inf' as a template variable name doesn't work because it isn't a valid variable name. Using 'nan' as a template variable name works OK:

>>> Template('{{ nan }}').render(Context({'nan': 'xxx'}))
u'xxx'

I think the fix is to allow variables named inf, rather than to support using inf as a float literal within templates.

[Levi Payne]

​WIP Pull Request

[Levi Payne]

Pull Request is ready for review.

[Fraser Nevett]

See also #28730

[Tim Graham <timograham@…>]

In 6c31042:

Refs #28721 -- Added test for variations of 'inf'/'infinity' as a template variable names.

Fixed by 9ec7d8e514e09636b0ab4bcac74b5f7a5be335a3.