ASCII array to number In Python

Question

I am trying to parse an array of ascii characters which form a number (float, int...) Sometimes array length is 1, 2, 3....8... I am looking for a way to get the whole array (with just one complete value each time) and return the number to add it to a json.

I am using python 3. Is there a fixed function to do that? I haven't found anything on the internet yet.

I was thinking in something like this:

return arrayBytes[0]<<8 | arrayBytes[1]

But I get values like 574 in a % value so it has to be wrong and just would work with 2 ascii array length.

Here you have an example of the input:

4 value: 0x32 0x38 0x2e 0x36
2 value 0x34 0x39 
3 value 0x30 0x2e 0x34

4 value: 0x32 0x38 0x2e 0x36, 2 value 0x34 0x39, 3 value 0x30 0x2e 0x34 — Biribu
– Biribu, Commented Aug 12, 2014 at 14:36
0x32 0x38 0x2e 0x36 is 28.6 as ASCII; are you sure these are not just numbers already? — Martijn Pieters
– Martijn Pieters, Commented Aug 12, 2014 at 14:38
They are numbers. I need to rejoin to get the 28.6 you printed — Biribu
– Biribu, Commented Aug 12, 2014 at 14:40

Martijn Pieters · Accepted Answer · 2014-08-12 15:30:53Z

1

You appear to have ASCII representations of numbers:

>>> '\x32\x38\x2e\x36'
'28.6'
>>> '\x34\x39'
'49'
>>> '\x30\x2e\x34'
'0.4'

Calling float() on these to turn them into Python float objects is enough:

>>> float('\x32\x38\x2e\x36')
28.6
>>> float('\x34\x39')
49.0
>>> float('\x30\x2e\x34')
0.4

If your input is integers, then they represent ASCII codepoints. In Python 3, use bytes() to quickly turn those back to text:

>>> bytes([50, 57, 46, 57])
b'29.9'
>>> bytes([50, 57, 46, 57]).decode('ascii')
'29.9'
>>> float(bytes([50, 57, 46, 57]))
29.9

In Python 2, use bytearray() instead:

>>> bytearray([50, 57, 46, 57])
bytearray(b'29.9')
>>> str(bytearray([50, 57, 46, 57]))
'29.9'
>>> bytearray([50, 57, 46, 57]).decode('ascii')
u'29.9'
>>> float(bytearray([50, 57, 46, 57]))
29.9

Either way you can go from list of integers to bytes, text or a floating point value with ease.

edited Aug 12, 2014 at 15:30

answered Aug 12, 2014 at 14:39

Martijn Pieters

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Comments

Strikeskids · Accepted Answer · 2014-08-12 14:42:10Z

0

You won't be able to use bitwise operations because those only work with small python integers. Instead you will need to multiply by the equivalent power of two.

mult = 1 << 8
answer = 0
for number in asciiBytes:
    answer *= mult
    answer += number

If you are just storing a string representation of the number, and not storing the number as the bitwise pieces separated, then call float(str) to turn the string into a number.

For example float('423.3') == 423.3

edited Aug 12, 2014 at 14:42

answered Aug 12, 2014 at 14:36

Strikeskids

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