not getting correct result from slicing strings in python

Question

I am slicing 24 digits long binary number into three 8digits long numbers. Here is my code below:

def extract_number(number):
    number_in_string = str(number)
    red = number_in_string[:8]
    green = number_in_string[8:16]
    blue = number_in_string[16:24]
    return [int(red), int(green), int(blue)]

if __name__ == '__main__':
    print(extract_number(101111010110011011100100))

The result i get from the terminal is

[10111101, 1100110, 11100100]

The problem occurs in the 2nd number. It's digit is not 8 digits long when I did number_in_string[8:16]. And I using slice function wrong here?

Konstantin · Accepted Answer · 2015-11-01 03:49:26Z

2

You use slice function correctly

In [28]: str(101111010110011011100100)[8:16]
Out[28]: '01100110'

The second number has leading zero which is omitted once you convert string to integer.

In [29]: int('01100110')
Out[29]: 1100110

You use numbers represented in decimal base, but mention binary base. Is there a reason for this? I would like to recommend you to use binary base

def extract_number(number):
    number_in_string = bin(number)[2:]
    red = number_in_string[:8]
    green = number_in_string[8:16]
    blue = number_in_string[16:24]
    return [int(red, 2), int(green, 2), int(blue, 2)]

if __name__ == '__main__':
    print(extract_number(0b101111010110011011100100))

The code above outputs

[189, 102, 228]

If you need binary representations of these numbers use builtin bin function

edited Nov 1, 2015 at 3:49

answered Nov 1, 2015 at 3:36

Konstantin

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Comments

Swastik Padhi · Accepted Answer · 2015-11-01 21:55:37Z

1

Try returning the strings as they are. Converting them to integers will remove any leading zeroes from the string, if present. Corrected code here-

def extract_number(number):
    number_in_string = str(number)
    red = number_in_string[:8]
    green = number_in_string[8:16]
    blue = number_in_string[16:24]
    return [red, green, blue]

if __name__ == '__main__':
    print(extract_number(101111010110011011100100))

Output-

['10111101', '01100110', '11100100']

edited Nov 1, 2015 at 21:55

answered Nov 1, 2015 at 3:38

Swastik Padhi

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3 Comments

Kahsn Over a year ago

Hey! I do not see any changes here 0_0

Swastik Padhi Over a year ago

@Kahsn I don't see why you don't see any changes. Check the answer again. I have updated it with the output. Note, I am returning the sliced strings without casting them to integers.

Kahsn Over a year ago

Oh my bad. I totally missed the int() part. Gottcha.

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