Python Regex - checking for a capital letter with a lowercase after

Question

I am trying to check for a capital letter that has a lowercase letter coming directly after it. The trick is that there is going to be a bunch of garbage capital letters and number coming directly before it. For example: ``` AASKH317298DIUANFProgramming is fun ``` as you can see, there is a bunch of stuff we don't need coming directly before the phrase we do need, `Programming is fun`. I am trying to use regex to do this by taking each string and then substituting it out with `''` as the original string does not have to be kept. ``` re.sub(r'^[A-Z0-9]*', '', string) ``` The problem with this code is that it leaves us with `rogramming is fun`, as the `P` is a capital letter. How would I go about checking to make sure that if the next letter is a lowercase, then I should leave that capital untouched. (The `P` in `Programming`)

Accepted Answer

Use a negative look-ahead:

```
re.sub(r'^[A-Z0-9]*(?![a-z])', '', string)
```

This matches any uppercase character or digit that is not followed by a lowercase character.

Demo:

```
>>> import re
>>> string = 'AASKH317298DIUANFProgramming is fun'
>>> re.sub(r'^[A-Z0-9]*(?![a-z])', '', string)
'Programming is fun'
```

Python Regex - checking for a capital letter with a lowercase after

Solution

Problem