How do I change the string representation of a Python class?
PythonStringPython 3.xPrintingPython Problem Overview
In Java, I can override the toString()
method of my class. Then Java's print function prints the string representation of the object defined by its toString()
. Is there a Python equivalent to Java's toString()
?
For example, I have a PlayCard class. I have an instance c of PlayCard. Now:
>>> print(c)
<__main__.Card object at 0x01FD5D30>
But what I want is something like:
>>> print(c)
A♣
How do I customize the string representation of my class instances?
I'm using Python 3.x
Python Solutions
Solution 1 - Python
The closest equivalent to Java's toString
is to implement __str__
for your class. Put this in your class definition:
def __str__(self):
return "foo"
You may also want to implement __repr__
to aid in debugging.
See here for more information:
Solution 2 - Python
This is not as easy as it seems, some core library functions don't work when only str is overwritten (checked with Python 2.7), see this thread for examples https://stackoverflow.com/questions/3768895/python-how-to-make-a-class-json-serializable Also, try this
import json
class A(unicode):
def __str__(self):
return 'a'
def __unicode__(self):
return u'a'
def __repr__(self):
return 'a'
a = A()
json.dumps(a)
produces
'""'
and not
'"a"'
as would be expected.
EDIT: answering mchicago's comment:
unicode does not have any attributes -- it is an immutable string, the value of which is hidden and not available from high-level Python code. The json
module uses re
for generating the string representation which seems to have access to this internal attribute. Here's a simple example to justify this:
b = A('b') print b
produces
'a'
while
json.dumps({'b': b})
produces
{"b": "b"}
so you see that the internal representation is used by some native libraries, probably for performance reasons.
See also this for more details: http://www.laurentluce.com/posts/python-string-objects-implementation/