On Wed, Oct 3, 2012 at 11:11 PM, boB Stepp <robertvst...@gmail.com> wrote:
>
> What happens if str() or repr() is not supported by a particular
> object? Is an exception thrown, an empty string returned or something
> else I am not imagining?
The __str__ method inherited from "object" calls __repr__.
For a class, __repr__ is inherited from type.__repr__, which returns
"<class 'module_name.class_name'>".
For an instance, __repr__ is inherited from object.__repr__, which returns
"<module_name.class_name object at address>".
If you override __str__ or __repr__, you must return a string. Else
the interpreter will raise a TypeError.
Basic example:
>>> class Test:...
repr of the class:
>>> repr(Test)
"<class '__main__.Test'>"
repr of an instance:
>>> repr(Test())
'<__main__.Test object at 0x958670c>'
> As I go along in my study of Python will it become clear to me when
> and how repr() and str() are being "...used, or implied in many
> places"?
str is Python's string type, while repr is a built-in function that
returns a string suitable for debugging.
You can also call str without an argument to get an empty string, i.e.
str() == ''. This is similar to other built-in types: int() == 0,
float() == 0.0, complex() == 0j, tuple() = (), list() = [], and dict =
{}. The returned value is either 0 or empty -- and boolean False in
all cases.
str also takes the optional arguments "encoding" and "errors" to
decode an encoded string:
>>> str(b'spam', encoding='ascii')
'spam'
bytes and bytearray objects have a decode() method that offers the
same functionality:
>>> b'spam'.decode('ascii')
'spam'
But other objects that support the buffer interface might not. For
example, take the following array.array with the ASCII encoded bytes
of "spam":
>>> arr = array.array('B', b'spam')
Here's the repr:
>>> arr
array('B', [115, 112, 97, 109])
Without an argument str just returns the repr of the array:
>>> print(arr)
array('B', [115, 112, 97, 109])
(The print function calls str.)
But we can tell str to treat the array as an ASCII encoded buffer:
>>> print(str(arr, 'ascii'))
spam
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