Text handling in Python 3
Python 3 uses two very different types:
bytes: intended to represent raw byte data. For more information on this type, please consult PEP 358.
str: a unicode character string
Choosing Between "bytes" and "str"
When choosing the type you want to use to work with text you have to ask yourself: do I manipulate characters or bytes (integers)? "A" is a character and 65 is an integer. Examples:
- a network socket manipulates bytes
- a text parser manipulates characters (uses lower, strip, etc. methods)
Iterating over "bytes"
It's important to note that the bytes iterator generates integers and not characters:
>>> for item in b'abc': ... print item 97 98 99
Comparing one bytes object to another works as expected:
>>> b'xyz' == b'xyz' True >>> b'xyz' == b'abc' False
However, it is important to note that the bytes type is completely distinct from the str type in Python 3, and comparisons between them do not work:
>>> b'xyz' == 'xyz' Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: can't compare bytes and str
This should make clearly evident some incomplete transitions. But it also means that you really can't mix then very well:
>>> L = ["1", b"1"] >>> "1" in L True >>> "2" in L Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: can't compare str and bytes
As mentioned earlier, getting an item of a bytes returns an integer, not a bytes object:
>>> b'xyz' == b'x' False >>> b'xyz' 120
bytes is mutable, and as a result, it's not hashable. Among other things, this means that bytes objects can't be used as keys in dictionaries.
Hacks and workarounds for this include:
Other solutions include:
create an immutable frozenbytes type
- avoid using hash
For historical information that may be useful in porting or maintaining remaining Python 2 systems, please see previous page revisions.