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'''Data transformation functions.
From bytes to a number, number to bytes, base64-like-encoding, etc.
'''
import math
import types
def bit_size(number):
"""Returns the number of bits required to hold a specific long number"""
return int(math.ceil(math.log(number, 2)))
def bytes2int(bytes):
"""Converts a list of bytes or an 8-bit string to an integer.
When using unicode strings, encode it to some encoding like UTF8 first.
>>> (((128 * 256) + 64) * 256) + 15
8405007
>>> l = [128, 64, 15]
>>> bytes2int(l) #same as bytes2int('\x80@\x0f')
8405007
"""
if not (type(bytes) is types.ListType or type(bytes) is types.StringType):
raise TypeError("You must pass a string or a list")
# Convert byte stream to integer
integer = 0
for byte in bytes:
integer *= 256
if type(byte) is types.StringType: byte = ord(byte)
integer += byte
return integer
def int2bytes(number, block_size=None):
r'''Converts a number to a string of bytes.
@param number: the number to convert
@param block_size: the number of bytes to output. If the number encoded to
bytes is less than this, the block will be zero-padded. When not given,
the returned block is not padded.
@throws OverflowError when block_size is given and the number takes up more
bytes than fit into the block.
>>> int2bytes(123456789)
'\x07[\xcd\x15'
>>> bytes2int(int2bytes(123456789))
123456789
>>> int2bytes(123456789, 6)
'\x00\x00\x07[\xcd\x15'
>>> bytes2int(int2bytes(123456789, 128))
123456789
>>> int2bytes(123456789, 3)
Traceback (most recent call last):
...
OverflowError: Needed 4 bytes for number, but block size is 3
'''
# Type checking
if type(number) not in (types.LongType, types.IntType):
raise TypeError("You must pass an integer for 'number', not %s" %
number.__class__)
# Do some bounds checking
if block_size is not None:
needed_bytes = int(math.ceil(bit_size(number) / 8.0))
if needed_bytes > block_size:
raise OverflowError('Needed %i bytes for number, but block size '
'is %i' % (needed_bytes, block_size))
# Convert the number to bytes.
bytes = []
while number > 0:
bytes.insert(0, chr(number & 0xFF))
number >>= 8
# Pad with zeroes to fill the block
if block_size is not None:
padding = (block_size - needed_bytes) * '\x00'
else:
padding = ''
return padding + ''.join(bytes)
def to64(number):
"""Converts a number in the range of 0 to 63 into base 64 digit
character in the range of '0'-'9', 'A'-'Z', 'a'-'z','-','_'.
>>> to64(10)
'A'
"""
if not (type(number) is types.LongType or type(number) is types.IntType):
raise TypeError("You must pass a long or an int")
if 0 <= number <= 9: #00-09 translates to '0' - '9'
return chr(number + 48)
if 10 <= number <= 35:
return chr(number + 55) #10-35 translates to 'A' - 'Z'
if 36 <= number <= 61:
return chr(number + 61) #36-61 translates to 'a' - 'z'
if number == 62: # 62 translates to '-' (minus)
return chr(45)
if number == 63: # 63 translates to '_' (underscore)
return chr(95)
raise ValueError(u'Invalid Base64 value: %i' % number)
def from64(number):
"""Converts an ordinal character value in the range of
0-9,A-Z,a-z,-,_ to a number in the range of 0-63.
>>> from64(49)
1
"""
if not (type(number) is types.LongType or type(number) is types.IntType):
raise TypeError("You must pass a long or an int")
if 48 <= number <= 57: #ord('0') - ord('9') translates to 0-9
return(number - 48)
if 65 <= number <= 90: #ord('A') - ord('Z') translates to 10-35
return(number - 55)
if 97 <= number <= 122: #ord('a') - ord('z') translates to 36-61
return(number - 61)
if number == 45: #ord('-') translates to 62
return(62)
if number == 95: #ord('_') translates to 63
return(63)
raise ValueError(u'Invalid Base64 value: %i' % number)
def int2str64(number):
"""Converts a number to a string of base64 encoded characters in
the range of '0'-'9','A'-'Z,'a'-'z','-','_'.
>>> int2str64(123456789)
'7MyqL'
"""
if not (type(number) is types.LongType or type(number) is types.IntType):
raise TypeError("You must pass a long or an int")
string = ""
while number > 0:
string = "%s%s" % (to64(number & 0x3F), string)
number /= 64
return string
def str642int(string):
"""Converts a base64 encoded string into an integer.
The chars of this string in in the range '0'-'9','A'-'Z','a'-'z','-','_'
>>> str642int('7MyqL')
123456789
"""
if not (type(string) is types.ListType or type(string) is types.StringType):
raise TypeError("You must pass a string or a list")
integer = 0
for byte in string:
integer *= 64
if type(byte) is types.StringType: byte = ord(byte)
integer += from64(byte)
return integer
if __name__ == '__main__':
import doctest
doctest.testmod()
|
