Python string slicing not getting intended values-CodePudding

I am trying to search for the sum of occurances of a substring within a string:

string = 'ABCDCDC'
sub_string = 'CDC'
for i in range(len(string)-len(sub_string)):
    print(string[i:len(substring)]

I am unsure why this is my output:

ABC
BC
C

Should'nt it be:

ABC
BCD
CDC
DCD
CDC

CodePudding user response：

You need to increment length i times to match len 3 elemnst see

string = 'ABCDCDC'
sub_string = 'CDC'
for i in range(len(string)-len(sub_string)):
   
    print(f'{i} to {len(sub_string)}')

in your case #

0 to 3
1 to 3
2 to 3
3 to 3

Code correction

string = 'ABCDCDC'
sub_string = 'CDC'
for i in range(len(string)-len(sub_string)):
    print(string[ i:i   len(substring)]
    print(f'{i} to {i len(sub_string)}')

output #

0 to 3
1 to 4
2 to 5
3 to 6

you will get

ABC
BCD
CDC
DCD

CodePudding user response：

A small change would get the expected output

Code:

string = 'ABCDCDC'
sub_string = 'CDC'
for i in range(len(string)-len(sub_string)):
    print(string[i: i  len(sub_string)])

Output

ABC
BCD
CDC
DCD

Reason:

You can try priniting the len(sub_string) and see that it is constanlt 3 because length is always 3.

string = 'ABCDCDC'
sub_string = 'CDC'
for i in range(len(string)-len(sub_string)):
    print(i, len(sub_string))

Output:

The change that we did was i len(sub_string) we are changing the end index by adding it to the start index

CodePudding user response：

You are using len(substring) instead of i len(substring).

string = 'ABCDCDC'
sub_string = 'CDC'
for i in range(len(string)-len(sub_string) 1):
    print(string[i:i   len(sub_string)])

output:

ABC
BCD
CDC
DCD
CDC

PS: use range(len(string)-len(sub_string) 1) to make the loop iterate over all possible, including the final index.

CodePudding user response：

You have missed two things when you pass a number in range() it is exclusive of that number so for that you should add 1 to that and you have missed to add i in iteration while slicing this code will work for you.

string = 'ABCDCDC'
sub_string = 'CDC'
for i in range(len(string)-len(sub_string) 1):
    print(string[i: i  len(sub_string)])