CODEWITHSUNDEEP
pythonregex
balderasric
balderasric

Reputation: 3

What is the difference in this re expressions?

i am testing the re expressions and the book example was:

if re.search('^X\S*: [0-9.]+', line):

But with my expression I reach the same result:

if re.search('^X\S*: [0-9]', line):

What's is the difference?, what do I not see?. Thank you.

Upvotes: 0

Views: 60

Answers (2)

jramm
jramm

Reputation: 821

If you are simply trying to match any line that begins with X: and a number, these are functionally equivalent within the context of your program. They will both find and match lines like these, and return TRUE for your IF statement:

X: 100
X: 9.23
X: 9912.2434.2424.2435
Xabc: 1
X-rf: 0.7

However, the patterns are not the same and if you use them in a different context, they may no longer be functionally equivalent. For example, if you need to match the entire line, you would have to use re.search('^X\S*: [0-9.]+', line). The other pattern, re.search('^X\S*: [0-9]', line), only will match a single digit 0-9 and nothing else after that.

Upvotes: 1

m0nhawk
m0nhawk

Reputation: 24168

This is two completely different regex expressions:

^X\S*: [0-9.]+
^X\S*: [0-9]

Comparing side-by-side yields the difference: [0-9.]+ vs [0-9].

The second one will only match one digit.

While the first one will match one number of digits and dots.

So, the second one will fail for the following examples:

X: 1.23
X: 123.3213.23131

And any other combination of digits + dot.

The same result will be only for something like this:

X: 1

Upvotes: 1

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