ascii2dec

[Uwe Mayer]

Hi,

this must sound stupid to you, but I'm ages out of Python and I just can't
find a function to convert 4 bytes of binary data to an integer value:

length=f.read(4) # get length in binary
length=socket.htonl(length) # swap bytes

#convert 4 bytes to integer

f.close()

Thanks for any help
Uwe
--

 

[Uwe Mayer]

this must sound stupid to you, but I'm ages out of Python and I just can't
find a function to convert 4 bytes of binary data to an integer value:

length=f.read(4) # get length in binary
length=socket.htonl(length) # swap bytes

#convert 4 bytes to integer

Sorry, socket.htonl(...) already expects a number, so its:

#convert 4 bytes to integer
length=socket.htonl(length) # swap bytes

i.e.
How to convert:

length = '\x01\x00\x00\x00'

to an integer

Uwe
--

 

[Fredrik Lundh]

this must sound stupid to you, but I'm ages out of Python and I just can't
find a function to convert 4 bytes of binary data to an integer value:

length=f.read(4) # get length in binary
length=socket.htonl(length) # swap bytes

#convert 4 bytes to integer

f.close()

Thanks for any help

import struct
result = struct.unpack("!i", f.read(4))
length = result[0]

where "!" means network byte order, and "i" means 32-bit integer.

see the struct documentation for more options.

if the f.read fails to read 4 bytes, this operation raises a struct.error
exception

note that unpack returns a tuple; you may prefer to unpack a bunch
of fields in one step:

width, height = struct.unpack("!ii", f.read(8))

</F>

 

[Peter Hansen]

Sorry, socket.htonl(...) already expects a number, so its:


i.e.
How to convert:

length = '\x01\x00\x00\x00'

to an integer

Use the struct module, with appropriate "endianism".

-Peter

 

[Sean Ross]

Uwe Mayer wrote:
How to convert:

length = '\x01\x00\x00\x00'

to an integer

As Peter suggested, use struct.unpack with the appropriate endianness, e.g.

import struct
length = '\x01\x00\x00\x00'
# convert 'length' to signed integer (big-endian)
unpacked = struct.unpack('>i', length)[0] # unpack returns a tuple
unpacked 16777216
# convert 'length' to signed integer (little-endian)
unpacked = struct.unpack('i', length)[0] # or, fmt = '<i'
unpacked

1

HTH
Sean