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I have constructed my own class User which has the property userID. I override the __repr__ so that it's the userID string.

In another class I have an array self.users = [] with a couple User instances. For testing purposes I gave them user ID's 1 and 2. I use:

'[%s]' % ','.join(map(str, self.users))

To print the contents of the array, producing:

[1,2]

I'm trying to make an if statement along the lines of:

if "1" in self.users:
  print "True"

Above is a simple representation of what I'm trying to achieve. I have tried many approaches and I can't get the program to print true. Does anyone know how to do this?

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    is the value in self.users an int? cause you're checking for the string '1'. Commented Nov 28, 2012 at 22:14
  • He's mapping the str constructor over the list. That's not the problem. Commented Nov 28, 2012 at 22:15
  • Out of curiosity, why are you mapping str over the list? Normally people do that to avoid the fact that list.__str__ calls __repr__ on each element—but in your case, you've defined __repr__, and you're specifically looking for the __repr__ value… Commented Nov 28, 2012 at 22:17
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    We're really just guessing what the elements in self.users are. We know they have well defined __str__/__repr__, but that's about it. In order to provide a better solution, you should insert a print self.users right before your if statement and post that result as an edit to your question Commented Nov 28, 2012 at 22:17
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    Is there a reason you need to search by string representation instead of the actual member variable? Why not just any(user.userID == '1' for user in self.users)? Commented Nov 28, 2012 at 22:21

3 Answers 3

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Do you want:

if any("1" in str(x) for x in self.users):
   print "True"

probably better is:

if any("1" == x.userID for x in self.users):
   print True

if I'm reading your post correctly.

Finally, depending on the API for User, you could use the ID in an equality test:

class User(object):
    def __eq__(self,other):
       return self.userID == other
   #other methods here

Now you can use __contains__ (in) on your list as you were trying to do initially:

if "1" in self.users:
   print "True"
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3 Comments

As I said to Blender, given that he's defined __repr__ rather than __str__, I'd use repr(x) here.
@abarnert -- Maybe. __str__ calls __repr__ by default though... (and I think that str is what should really be used here. I would contend that OP should re-think the decision to override __repr__ in this way)
Yes, assuming he didn't define that as well (or doesn't do so later). As Blender points out, it's probably better to change his __repr__ to __str__ in the first place. But either way, I think it makes sense to search for the one you made sure to define…
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"1" in self.users checks to see if the string "1" is in the list self.users. You're trying to check if there exists a user whose string representation is "1", so you could try something like this:

if '1' in map(str, self.users):
    print 'True

Also, I'd change __repr__ to __str__ in your class definition.

__repr__ usually returns a string that can be eval()uated back into the original object, while __str__ returns a human-readable representation of the object. You're doing the latter, so I suggest you use __str__ instead of __repr__.

I'd read through this question as well: Difference between __str__ and __repr__ in Python

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3 Comments

Given that he's defined __repr__ rather than __str__, I'd use repr rather than str here.
itertools.imap is better here as it is more accommodating of short-cicuiting
Yes, I think that's a more reasonable fix in general. And in particular, he chose to map str rather than repr over the list, which implies that he actually wants this to be the str representation anyway.
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From your problem definition, it sounds like you're trying to find if you have any users whose userID attribute is '1'.

The fact that your __repr__ function happens to use the userID as the representation does mean that's the best way to search for it. Why not just this?

if any(user.userID == '1' for user in self.users):
    print "True"

If you really do need to search for the string representation, of course, use the answer posted by mgilson or Blender (and figure out which of str and repr you want). But if it's not necessary, don't do it.

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