How to convert byte array value to float In Python

Question

I have a list [142, 65, 110, 51] it needs to be converted to a float similar to c_float from ctypes lib. I don't know the logic for c_float.

I am trying to use module struct:

import struct

x = [142, 65, 110, 51]
ans = 0
for i, v in enumerate(x):
    ans += (v << (8 * i))

combined = ans  # 862863758

buf = struct.pack("d", combined)

fl = struct.unpack("ff", buf)
print(fl)

I get (-32768.0, 25.21441650390625), but I need a single float value.

In short I want something like [142, 65, 110, 51] => 0.0003232(some float value).

"but i need a single float value" - which one in this case ? — TheEagle
– TheEagle, Commented Jan 21, 2021 at 11:56
@frederic single value means [142, 65, 110, 51] => 0.0003232 something like that. — ooo
– ooo, Commented Jan 21, 2021 at 11:58
There are numerous functions which will map 4 bytes to a float. Are you looking for a specific float (e.g. the one in which those bytes are its underlying representation as an IEEE single-precision float)? "something like" is too vague to work with. — John Coleman
– John Coleman, Commented Jan 21, 2021 at 12:06
@JohnColeman I am looking for similar technique as c_float from ctypes python lib. — ooo
– ooo, Commented Jan 21, 2021 at 12:10

John Coleman · Accepted Answer · 2021-01-21 12:17:01Z

4

Use f rather than ff:

import struct

x = [142, 65, 110, 51]
fl = struct.unpack("f", bytes(x))
print(fl)

Which prints (5.54733148305786e-08,)

Note that you can skip your ans variable completely and directly convert x to a bytes object which can be unpacked.

answered Jan 21, 2021 at 12:17

John Coleman

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Lior Cohen · Accepted Answer · 2021-01-21 12:13:45Z

3

import struct

x =  [142, 65, 110, 51]
ans = 0
for i, v in enumerate(x):
    ans += (v << (8 * i))

combined = ans  # 862863758

buf = struct.pack("I", combined)
fl = struct.unpack("f", buf)
print(fl[0])  #  --> 5.54733148305786e-08

answered Jan 21, 2021 at 12:13

Lior Cohen

5,7202 gold badges18 silver badges33 bronze badges

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