Printing a list of objects

Question

I am a Python newbie. I have this small problem. I want to print a list of objects but all it prints is some weird internal representation of object. I have even defined __str__ method but still I am getting this weird output. What am I missing here?

class person(object):
  def __init__(self, name, age):
    self.name = name
    self.age = age

  def __str__(self):
     return self.name + "(" + str(self.age) + ")"

def partition(coll, pred):
  left = []
  right = []
  for c in coll:
    if pred(c):
      left.append(c)
    else:
      right.append(c)
  return left, right


people = [
  person("Cheryl", 20),
  person("Shemoor", 14 ),
  person("Kimbala", 25),
  person("Sakharam", 8)
]

young_fellas, old_fellas = partition(people, lambda p : p.age < 18)
print(young_fellas)
print(old_fellas)

Please note that I know I can use either a for loop or a map function here. I am looking for something shorter and more idiomatic. Thanks.

EDIT:

One more question: Is the above code of mine Pythonic?

score 7 · Accepted Answer · edited May 23 '17 at 12:13

7

Unless you're explicitly converting to a str, it's the __repr__ method that's used to render your objects.

See Difference between __str__ and __repr__ in Python for more details.

edited May 23 '17 at 12:13

Community

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1

answered Jul 17 '10 at 15:31

Blair Conrad

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Thank you! Though you'll still have to wait for 8 minutes for the green cookie. :-) – one-zero-zero-one Jul 17 '10 at 15:36

score 2 · Answer 2 · answered Jul 17 '10 at 17:20

2

Your made this object:

person("Cheryl", 20)

This means repr should be same after creation:

def __repr__(self):
 return 'person(%r,%r)' % (self.name,self.age)

Output becomes:

[person('Shemoor',14), person('Sakharam',8)]
[person('Cheryl',20), person('Kimbala',25)]

answered Jul 17 '10 at 17:20

Tony Veijalainen

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You are welcome. Nice function you have written, this partition. I am a string partition fan myself and I dig it. – Tony Veijalainen Jul 17 '10 at 22:26
++: Comes with the bonus that the output can directly be fed back into python (what the idea of repr() is anyway) – Nas Banov Jul 17 '10 at 23:20

score 1 · Answer 3 · answered Jul 17 '10 at 15:33

1

You could do:

print(map(str,young_fellas))

answered Jul 17 '10 at 15:33

SiggyF

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About the pythonic part, there's a section on that in the docs. You could use the repr(lib) to create your own debug representation. In this case person("name",1) is a better representation than person(name,1) because it should look like a valid Python expression that could be used to recreate an object. http://docs.python.org/reference/datamodel.html#object.__repr__ http://www.python.org/dev/peps/pep-0008/ – SiggyF Jul 17 '10 at 15:49

st0le · Answer 4 · 2010-07-17T17:36:09.177

0

try overriding repr

  def __repr__(self):
      return self.name + "(" + str(self.age) + ")"

Edit: Better way, Thanks to Paul.

  def __repr__(self):
     return "%s(%d)" % (self.name, self.age)

edited Jul 17 '10 at 17:36

answered Jul 17 '10 at 15:33

st0le

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String interpolation `"%s(%d)" % (self.name, self.age)` or `''.join(list_of_string_bits)` are better styles to learn than adding up little bits of strings using '+'. – PaulMcG Jul 17 '10 at 16:15
1

@Paul McGuire: in this particular case not really, so don't troll it :) – Nas Banov Jul 17 '10 at 23:18

Printing a list of objects

4 Answers4