How to convert int to signed char?

Question

Let's say I have integer x (-128 <= x <= 127). How to convert x to signed char?

I did like this. But I couldn't.

>>> x = -1
>>> chr(x)
ValueError: chr() arg not in range(256)

Answer 1

Within Python, there aren't really any borders between signed, unsigned, char, int, long, etc. However, if your aim is to serialize data to use with a C module, function, or whatever, you can use the struct module to pack and unpack data. b, for example, packs data as a signed char type.

>>> import struct
>>> struct.pack('bbb', 1, -2, 4)
b'\x01\xfe\x04'

If you're directly talking to a C function, use ctypes types as Ashwin suggests; when you pass them Python translates them as appropriate and piles them on the stack.

Answer 2

It does not work, because x is not between 0 and 256.

chr must be given an int between 0 and 256.

Answer 3

In Python 3, chr() does not convert an int into a signed char (which Python doesn't have anyway). chr() returns a Unicode string having the ordinal value of the inputted int.

>>> chr(77)
'M'
>>> chr(690)
'ʲ'

The input can be a number in any supported base, not just decimal:

>>> chr(0xBAFF)
'뫿'

Note: In Python 2, the int must be between 0 and 255, and will output a standard (non-Unicode) string. unichr() in Py2 behaves as above.