I'm trying to write a simple function in python to do what in or str.contains does, here are the codes:
def contains(big, little):
length = len(little_string)
for i in big:
if big[i:i+length-1] == little:
return True
return False
For line if big[i:i+length-1] == little:`` it throws a TypeError saying must be str not int and I'm baffled. Since I think as long as big is a string the slicing of it will certainly be string too.
Does anyone know why this happened? thanks a lot.
I think what you're looking for is to iterate over a range, not over the string big itself:
big = 'abcd'
for i in big:
print(i)
a
b
c
d
for i in range(len(big)):
print(i)
0
1
2
3
This is what's causing your error, you are passing characters of big into your slice and then adding them to int. The TypeError is from the addition of the two, not the slice:
'a' + 1
TypeError: must be str, not int
big = 'abcd'
big['a': 'a'+1]
TypeError: must be str, not int
To fix this, create a range(len(big)) which produces those integer indices, which match the types, and the slice will work:
def contains(big, little):
l = len(little)
## Do this instead
# i is now an int in the range of len(big)
for i in range(len(big)):
if b[i:i + l] == little:
return True
return False
You also don't need the -1 in your slice, since slicing will not produce an IndexError
There are couple of little errors in the code you show us. For starters, a typo where you calculate len(little_string) while your parameter is called little.
The core of the issue as you describe is because for in in big effectively loops through the characters of the big string, which is not what you want to do in the code. Since you are looking at moving by index, then you should rather do something like this:
def contains(big, little):
length = len(little) # fix the typo
for i in range(len(big)): # this generates list of indices [0,1,2...]
if big[i:i + length] == little: # note we fixed it removing -1
return True
return False
# test
needle = 'one'
haystack = 'dragone'
print(contains(haystack, needle))
>> True
bigis astr, thenfor i in bigwill yield characters of the stringfor i in len(big).for i in range(len(big)).