AttributeError: ‘str’ object has no attribute ‘digits’

March 14, 2011

‘str’ object has no attribute ‘digits’

On silly ways you can puzzle yourself – part 412

Summary

How to make Python report that a string object has no attribute ‘digits’

Confusing Yourself – the easy way


Today I was working on a little piece of code which I hadn’t originally written and which looked something like this :

import string
def foo(string):
  for c in string:
    if c in string.digits:
       #do something

As is well known the Python string module contains a number of useful constants one of which is string.digits

>>> import string
>>> print string.digits
0123456789

Missing ‘digits’

My problem was that every time I went to execute this code it got to the reference to string.digits and the Python intepreter would report

AttributeError: 'str' object has no attribute 'digits'

I spent a happy half hour looking backwards and forwards trying to understand why the String module might think it had no attribute ‘digits’ when everything indicated quite clearly it did until I realised what the problem was.

def foo(string):

That argument name ‘string’ had carefully chucked away my previous reference to the String module and as a string has no attribute ‘digits’ the intpreter was quite reasonably complaining !

My defense

In my defense I wouldn’t normally use variable names, like ‘string’,  that come quite that close to commonly used modules but then like I say I didn’t write the original function

… but what I should have done

But then again what I should have done a great deal sooner than I did was to add a couple of lines to the function so that it read :

import string
import pprint
def foo(string):
  for c in string:
    pprint.pprint(dir(string))
    if c in string.digits:
       #do something

which would have output something like this

['__add__',
 '__class__',
 '__contains__',
 '__delattr__',
 '__doc__',
 '__eq__',
 '__format__',
 '__ge__',
 '__getattribute__',
 '__getitem__',
 '__getnewargs__',
 '__getslice__',
 '__gt__',
 '__hash__',
 '__init__',
 '__le__',
 '__len__',
 '__lt__',
 '__mod__',
 '__mul__',
 '__ne__',
 '__new__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__rmod__',
 '__rmul__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 '_formatter_field_name_split',
 '_formatter_parser',
 'capitalize',
 'center',
 'count',
 'decode',
 'encode',
 'endswith',
 'expandtabs',
 'find',
 'format',
 'index',
 'isalnum',
 'isalpha',
 'isdigit',
 'islower',
 'isspace',
 'istitle',
 'isupper',
 'join',
 'ljust',
 'lower',
 'lstrip',
 'partition',
 'replace',
 'rfind',
 'rindex',
 'rjust',
 'rpartition',
 'rsplit',
 'rstrip',
 'split',
 'splitlines',
 'startswith',
 'strip',
 'swapcase',
 'title',
 'translate',
 'upper',
 'zfill']

… and made it pretty clear that things were not as I thought they were.

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