🔒 Understanding the difference between index & find method

[small marten]

What's the difference between the .index and .find string method? As far I've learned I can use index with [start:end:step] Can't we just use the .find string method in the image?

[narrow grove]

@small marten

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[sick flicker]

!d str.index

[narrow grove]

str.index

str.index(sub[, start[, end]])```
Like [`find()`](https://docs.python.org/3/library/stdtypes.html#str.find), but raise [`ValueError`](https://docs.python.org/3/library/exceptions.html#ValueError) when the substring is not found.

[sick flicker]

!d str.find

[narrow grove]

str.find

str.find(sub[, start[, end]])```
Return the lowest index in the string where substring *sub* is found within the slice `s[start:end]`. Optional arguments *start* and *end* are interpreted as in slice notation. Return `-1` if *sub* is not found.

Note

The [`find()`](https://docs.python.org/3/library/stdtypes.html#str.find) method should be used only if you need to know the position of *sub*. To check if *sub* is a substring or not, use the [`in`](https://docs.python.org/3/reference/expressions.html#in) operator:

```py
>>> 'Py' in 'Python'
True

[near spindle]

str.index and str.find seem to do the same thing.

Aha, the value error.

[sick flicker]

!e py text = 'abc' print(text.find('d'))

[narrow grove]

:white_check_mark: Your 3.12 eval job has completed with return code 0.

-1

[sick flicker]

!e py text = 'abc' text.index('d')

[narrow grove]

:x: Your 3.12 eval job has completed with return code 1.

001 | Traceback (most recent call last):
002 |   File "/home/main.py", line 2, in <module>
003 |     text.index('d')
004 | ValueError: substring not found

[sick flicker]

I dislike str.find.

[near spindle]

It's handy for for-loops: while str.find(..) >= 0 do thing, advance

Sorry, while loops and similar.

[sick flicker]

"Hey, Python, where is 'd' in 'abc'? Oh, it's where 'c' is? Okay, cool."

[near spindle]

You're conflating "index out of range" with "Python negative list indices". They are different ideas.

[sick flicker]

Allow me my spite.

[near spindle]

These methods are from the Dawn Times, and APIs more closely resembled C. Where a -1 is a common return value for not-found/invalid.

[narrow grove]

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