I'm python beginner. I wrote this code but it can't work successfully. Someone can understand why?
if __name__ == '__main__':
# if "pro" begin with "test", delete "test" from "pro".
pro = "001001111010010101001"
test = "0010"
if pro.startswith(test):
pro = pro.lstrip(test)
# My ideal -> pro == "01111010010101001"
print pro
print pro
This code doesn't output anything.
str.lstrip() removes all characters that appear in the set of characters you gave it. Since you gave it both 0 and 1 in that set, and the string consists of only zeros and ones, you removed the whole string.
In other words, str.lstrip() does not remove a prefix. It removes one character at a time, provided that character is named in the argument:
>>> '0123'.lstrip('0')
'123'
>>> '0123'.lstrip('10')
'23'
>>> '0123'.lstrip('20')
'123'
Remove the first len(test) characters instead:
pro = pro[len(test):]
lstrip(chars) returns a copy of the string in which all chars have been stripped from the beginning of the string. so if you pass test that contain 1,0 it remove all the characters from pro (pro contain only 0,1) .
>>> pro = pro.lstrip('10')
>>> pro
''
instead you can Just use slicing :
>>> if pro.startswith(test):
... pro=pro[len(test):]
...
>>> pro
'01111010010101001'
This is because lstrip removes all of the left characters from the set given so removes everything:
I think that you need:
pro = pro.startswith(test) and pro[len(test):] or pro
this will remove test from the start of pro if it is there.
pro[len(test):] if pro.startswith(test) else pro.Just as extra.. This will also work:
>>> pro = "001001111010010101001"
>>> test = "0010"
>>> if pro.startswith(test):
pro = pro.partition(test)[-1]
print pro
01111010010101001
pro = pro[len(test):] might be more clear than using pro.partition().