CODEWITHSUNDEEP
python
perplex
perplex

Reputation: 159

Find the value of a String in i-th position

I have a binary String. I add 1 at every 7-th position in that string. Using the following code.

 binary='1010010110000110100101100001'
 # insert 1 after every 7 bit.
 new_binary='1'.join(binary[i:i+7] for i in range(0, len(binary), 7))
 print(new_binary)

my output String:

1010010111000011101001011100001

Now I want to remove those extra 1 from the output string and get back the Original String. For that I try to identify the position of those 1 I tried the following approach:

binary='1010010111000011101001011100001'
# remove 1 after every 7 bit.
for i in range(0, len(binary), 7):
if((i+7) <len(binary)):
    print("current position = ",i+7, "Value of the position: ", binary[i+7])
    print("\n")

and my current output is: 

('current position = ', 7, 'Value of the position: ', '1')
('current position = ', 14, 'Value of the position: ', '1')
('current position = ', 21, 'Value of the position: ', '1')
('current position = ', 28, 'Value of the position: ', '0')

now from the output, you can see that the first output is OK. But for the 2nd output, 'current position = ' should be 15 instead of 14. and the 3rd output should be 23 instead of 21. And there should be no 4th output. Any help regarding this. please.

N.B: I'm trying to do this for a larger bit string.

Upvotes: 1

Views: 243

Answers (1)

Jean-Fran&#231;ois Fabre
Jean-Fran&#231;ois Fabre

Reputation: 140307

the opposite transform needs you to have a step of 7+1 to remove the extra 1 added every 7 characters.

You can print the correct position by printing the 7th character every 8 characters, like this:

for i in range(0, len(new_binary), 8):
  if((i+8) <len(new_binary)):
    print("current position = ",i+7, "Value of the position: ", new_binary[i+7])
    print("\n")

Now, how to retrieve the original string?

This can be done with the "inverse" comprehension you used to create the first string.

binary='1010010110000110100101100001'
# insert 1 after every 7 bit.
new_binary='1'.join(binary[i:i+7] for i in range(0, len(binary), 7))
print(new_binary)

old_binary = "".join(new_binary[i:i+7] for i in range(0, len(new_binary), 8))
print(old_binary==binary)

prints True :)

Upvotes: 1

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