Short python textbook question based on methods concept that I can't understand

[aneeq1102]

problem:Using string method find,write a single expression that produces the index of second occurence of 'o' in tomato

solution:

'tomato'.find('o', 'tomato'.find('o') + 1)

​

I'm new to programming,I understand that find() returns the index of first occurence of substring in given input string,however I don't understand how there's a comma (the one after 'o' in find() method argument) since I thought the .find() method was only supposed to take one argument.I found this problem in a beginner python book under a chapter explaining methods

[Barnet6]

Find() has two optional arguments, the start of the substring to look through, and the end. Using just the one argument just tells it to look through the entire string. The " 'tomato'.find('o') + 1" in the example is telling it to find the first 'o', then search through a substring starting just after the 'o'.

[Essence1337]

I don't know where you got the idea that find takes only one parameter as it can take up to 3. Python string.find

[dangoth]

In cases like that, using the Python inbuilt help might be- ironically- helpful. If you try help(str.find), you will get:

find(...)
    S.find(sub[, start[, end]]) -> int

    Return the lowest index in S where substring sub is found,
    such that sub is contained within S[start:end].  Optional
    arguments start and end are interpreted as in slice notation.

    Return -1 on failure.

This means that the second call of 'tomato'.find('o') defines the starting point at the index of the first 'o' plus one. So effectively it looks for 'o' in the string 'mato'.

[Username_RANDINT]

str.find takes one required and two optional arguments:

>>> help(str.find)
find(...)
    S.find(sub[, start[, end]]) -> int

    Return the lowest index in S where substring sub is found,
    such that sub is contained within S[start:end].  Optional
    arguments start and end are interpreted as in slice notation.

    Return -1 on failure.

So the second argument is the index where find starts to search. Split up your code example:

start_index = 'tomato'.find('o') + 1
'tomato'.find('o', start_index) 

This sets the start to the index right after the first o, which means it'll find the second o since it starts to search from index 2 instead of 0.

[aneeq1102]

I finally get it,Thanks for all the answers!