When I am in the Python or IPython console, what is called when I am returned an output?
For example,
python
>> x = 1
>> x
1
I'm curious about what method/function on x is returning 1. I'm asking because I'm seeing differences between calling print x and simply x .
Similary, is there a way to specify what is called? Does this configuration exist in IPython?
When you inspect an object in that manner in a REPL, it invokes the object's __repr__ method. In comparison, print uses the object's __str__ method. Example:
>>> class Widget:
... def __repr__(self):
... return "repr of a Widget"
... def __str__(self):
... return "str of a Widget"
...
>>> x = Widget()
>>> x
repr of a Widget
>>> print x
str of a Widget
>>> print [x,2,3]
[repr of a Widget, 2, 3]
>>> print repr(x)
repr of a Widget
>>> print str(x)
str of a Widget
When defining __repr__ and __str__ for your own classes, try to follow the documentation's suggestions regarding which one should be more detailed and "official".
[ __repr__ computes] the “official” string representation of an object. If at all possible, this should look like a valid Python expression that could be used to recreate an object with the same value (given an appropriate environment).
...
[ __str__ computes] the “informal” string representation of an object. This differs from __repr__() in that it does not have to be a valid Python expression: a more convenient or concise representation may be used instead.
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