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Python Regular Expressions in Python Introduction to Regular Expressions Reading Files

Andrei Oprescu
Andrei Oprescu
9,547 Points
Posted by Andrei Oprescu
Andrei Oprescu
9,547 Points

I don't quite understand how this works

Hi!

I have watched the video and I had a confusion on this line of code: 'print(re.match(r'Kenneth', data))'

I don't understand how this code would know what to return because the code says that it will return a pattern that it will find. What pattern is that?

Thanks!

Andrei

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,457 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points

In this case, the pattern is a fixed string "Kenneth", so the matched string is the same as the pattern string.

Using re.match in this manner results in a basic "does string exist in data". Notice the output shows "span={0, 4)" for matching "Love" and "span=(6, 13)" for matching "Kenneth". These represent the character indexes of the match. So data[0:4] would be "Love" and data[6:13] would be "Kenneth".

Post back if you have more questions. Good luck!!

Andrei Oprescu
Andrei Oprescu
9,547 Points
Andrei Oprescu
Andrei Oprescu
9,547 Points

Hi Chris!

I have read you answer and it was helpful but can you tell me also how does python know where to look in memory to find this pattern? Surely these patterns are based on some criterias.

Thanks!

Andrei

Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points

The pattern is built from the first argument, "Kenneth" in this case, and is stored internally to the re.search method. The actual internal logic engine or state machine isn't viewable.

In words, i would read it as “Looking for a K, followed by an e, followed by an n,.....” and so on.

This pattern is compared to the data by scanning each character in the data for a match the the first pattern character. If it is a match, then compate then next two characters. If the pattern is broken, then then scanning starts again with the next data character.

I hope i understood your question correctly.

Andrei Oprescu
Andrei Oprescu
9,547 Points
Andrei Oprescu
Andrei Oprescu
9,547 Points

Hi again!

What I meant I don't understand is how does the code 're.match(r'Kenneth', data)' Give the result 'Love in return.

I hope you understood my question:).

Thanks!

Andrei

Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points

Ah. It doesn’t match both. In the video, there are two searches, one for r'Love' and one for r'Kenneth'. Each one independently finding the corresponding pattern in the data.

Andrei Oprescu
Andrei Oprescu
9,547 Points
Andrei Oprescu
Andrei Oprescu
9,547 Points

But how does this code give us this answer? It could have given us any other word from that .txt file.

Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points

A pattern that consists solely of a string can only imagine exactly that same sequence of characters so no other word could possibly be returned.