Confusing error w/ Python 3 and templates that use iteritems() #150

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samatjain opened this Issue Sep 26, 2012 · 3 comments

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@samatjain

Consider:

#!/usr/bin/env python3

from collections import OrderedDict

import jinja2

t = '''
{% for key, value in d.iteritems() %}
* {{ key }}: {{ value }}
{% endfor %}
'''

jt = jinja2.Template(t)

d = OrderedDict()
d['one'] = 1
d['two'] = 2
d['three'] = 3

print(jt.render(d=d))

When run w/ Python 3, you get an confusing exception:

Traceback (most recent call last):
  File "jinja2-OrderedDict.py", line 20, in <module>
    print(jt.render(d=d))
  File "/usr/lib/python3/dist-packages/jinja2/environment.py", line 895, in render
    return self.environment.handle_exception(exc_info, True)
  File "/usr/lib/python3/dist-packages/jinja2/environment.py", line 671, in handle_exception
    raise exc_value.with_traceback(tb)
  File "<template>", line 2, in <module>
jinja2.exceptions.UndefinedError: b"'collections.OrderedDict object' has no attribute 'iteritems'"

This is because the template uses iteritems, which is removed in Python 3. From the above exception, it's not clear the problem is in the template—it should be.

It works for normal Python 3 dictionaries because lines 205–210 of Jinja2 v2.61 add back an iteritems method:

    # not available on python 3
    if hasattr(dict, 'iterkeys'):
        iterkeys = _all('iterkeys')
        itervalues = _all('itervalues')
        iteritems = _all('iteritems')
    del _all

What's the best way to fix this? Better detect dict-like objects, try to spit out a better error, etc?

@mitsuhiko
Member

Dictionaries do not have iteritem methods in 3.x. You will need to change to .items(). Nothing I can do about that.

@mitsuhiko mitsuhiko closed this May 20, 2013
@wryfi
wryfi commented Mar 20, 2017

It would be nice if there were a built-in filter for this and other python 2to3 oddities.

@ThiefMaster
Member

Unless you have huge dicts, using .items() is not /that/ bad

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