repr() returned non-string

Question

So I have a class method with which I would like to draw out the dictionary and it's values:

 def __repr__ (self): 
        for row in zip(*([ky]+map(str,val) for ky,val in (self.slovar.items()))):

           print"\t".join (row)

If it's like this, I get a desired output:

>>> test
n   n1  n2
1   a   2.3
2   b   2.1
3   d   2.5

Traceback (most recent call last):
  File "<pyshell#521>", line 1, in <module>
    test
TypeError: __repr__ returned non-string (type NoneType)

but also a Traceback error.

If I return the value instead of printing it out, I only get this:

>>> test
n   n1  n2

It works fine if I make a custom method not the default 'system' one... (and I need it to be default)

You should not be `print`ing inside your `__repr__`. – Waleed Khan Dec 05 '12 at 14:36 — Waleed Khan, Dec 05 '12 at 14:36

score 12 · Answer 1 · answered Dec 05 '12 at 14:36

12

Your __repr__ method is using print to output information, but has no return statement, so it is effectively returning None, which is not a string.

What you could do is:

def __repr__ (self): 
    parts = []
    for row in zip(*([ky]+map(str,val) for ky,val in (self.slovar.items()))):
       parts.append("\t".join (row))
    return '\n'.join(parts)

You might also want to have a look at the pprint module.

answered Dec 05 '12 at 14:36

Thomas Orozco

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yes, I know. if I return instead of print, I only get the dictionary key names, and no items... – user1509923 Dec 05 '12 at 14:37
1

@user1509923 I added an example of how you could actually return something – Thomas Orozco Dec 05 '12 at 14:38

score 2 · Answer 2 · edited Dec 05 '12 at 14:44

2

your __repr__(self) method must return a string:

def __repr__ (self): 
 return "\n".join("\t".join (row) for row in zip(*([ky]+map(str,val) for ky,val in (self.slovar.items()))))

edited Dec 05 '12 at 14:44

glglgl

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answered Dec 05 '12 at 14:37

ptitpoulpe

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score 1 · Answer 3 · answered Dec 05 '12 at 14:44

1

You could do it like this:

def __repr__ (self): 
    rows = zip(*([ky]+map(str,val) for ky,val in (self.slovar.items())))
    return "\n".join("\t".join(row) for row in rows)

This way it remains readable and compact.

answered Dec 05 '12 at 14:44

glglgl

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__repr__() returned non-string

3 Answers3

repr() returned non-string