CODEWITHSUNDEEP
python-3.xdata-structuresgray-code
Pulkit Jain
Pulkit Jain

Reputation: 23

Can anybody explain me print statement in this code?

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()

Upvotes: -4

Views: 67

Answers (2)

Nevus
Nevus

Reputation: 1417

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.

Upvotes: 0

shuberman
shuberman

Reputation: 1490

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.

Upvotes: 0

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