Python 2.x
Python 2.x has two types that can be used to store a string:
str: raw byte data; each element represents a single byte, which can range in value from 0-255. This is the default type for string literals, which is widely considered to be a mistake due to the encoding problems it raises (for more information, see Joel Spolsky's [http://www.joelonsoftware.com/articles/Unicode.html The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets]).
unicode: a string in which each element represents a unicode character.
Both classes have the same methods and are very similar.
Python 3000
Python 3000 uses two very different types:
bytes: similar, but not identical, to Python 2.x's str type. It is intended to represent raw byte data. For more information on this type, please consult [http://www.python.org/dev/peps/pep-0358/ PEP 358].
str: a unicode character string which is exactly the same type as Python 2.x's unicode type.
Differences Between Python 2.x's "str" and Python 3000's "bytes"
Differences between Python 2.x's str and Python 3000's bytesinclude:
str is immutable, whereas bytes is mutable.
bytes "lacks" many methods present in str: strip(), lstrip(), rstrip(), lower(), upper(), splitlines(), etc.
indexing an item of a bytes object yields an integer, not a bytes object--for instance, b'xyz'[0] is the integer 120. On the other hand, indexing an item of a Python 2.x str yields another str instance.
Choosing Between "bytes" and "str"
When you migrate from Python 2.x to Python 3000, 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 (use lower, strip, etc. methods)
bytes and loops (for)
The following code will display 97, 98, 99 since the bytes iterator generates integer and not character!
for item in b'abc':
print item
compare bytes
>>> b'xyz' == b'xyz' # case 1 True >>> b'xyz' == 'xyz' # case 2 False >>> b'xyz'[0] == b'x' # case 3 False >>> b'xyz'[0] 120
Case 2 shows that bytes and unicode are never equals since they are different types. Case 3 shows an important point: getting an item of a bytes returns an integer (120) and not a bytes (len=1). This behaviour is different than Python 2.x:
# In Python 2.x
>>> "xyz"[0]
'x'
>>> type("xyz"), type("xyz"[0])
(<type 'str'>, <type 'str'>)
open issues
hash(bytes)
bytes is mutable and so it's not hashable. Hacks/Workaorounds:
- use buffer(value)
- use str8(value)
Other solutions:
- create frozenbytes type
- avoid using hash
Hash is used when bytes is a dictionary key.