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I found this code on internet but I am not able to understand how the print statement is working.

I have already tried to see many answers but none answers it perfectly.

def main():
    n=int(raw_input())
    for i in range(0, 1<<n):
        gray=i^(i>>1)
        print "{0:0{1}b}".format(gray,n),

main()
Pulkit Jain
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2 Answers2

0

What you are looking at is known by the concept of Advanced string formatting. Specifically, PEP 3101 Advanced string Formatting

You may refer the official documentation for understanding purposes.

shuberman
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0

for i in range(0, 1<<n):
Here, 1 << n shifts 1 by n bits to left. It means:
if n = 1, 1 << 1 would be 10, n = 2, 1 << 10 would be 100 [2 = binary 10]
and so on.
For decimal number the answer is equivalent 2 to the power n.
For binary 'n' number of zeros are added.
So the range is for i in range(0, 2 ** n). 

gray=i^(i>>1)

Here i>>1 shifts i by 1 bit to right. It means: 

   if i = 1, 1 >> 1 would be 0,    
       i = 2, 10 >> 1 would be 1 [2 = binary 10]   
       i = 3, 100 >> 1 would be 10 (in binary) 2 in decimal

and so on.
For decimal numbers it is equivalent to dividing by 2 (and ignoring digits after . decimal point).
For binary last digit is erased.

^ is exclusive OR operator. It is defined as: 

0 ^ 0 = 0,     
0 ^ 1 = 1 ^ 0 = 1,   
1 ^ 1 = 0  

print "{0:0{1}b}".format(gray,n)

Here {1} refers to n, b refers to binary. So gray is converted to binary and expressed in n digits.

Nevus
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  • You may see [Int to binary](https://stackoverflow.com/questions/699866/python-int-to-binary-string) or [Format specs](https://docs.python.org/3/library/string.html#formatspec) – Nevus Aug 17 '19 at 11:27