Python Regular Expression [\d+]

Question

I am working on regular expression python, I came across this problem.

A valid mobile number is a ten digit number starting with a 7,8 or 9. my solution to this was :

if len(x)==10 and re.search(r'^[7|8|9]+[\d+]$',x):

for which i was getting error. later I changed it to

if len(x)==10 and re.search(r'^[7|8|9]+\d+$',x):

for which all test cases passed. I want to know what the difference between using and not using [] for \d+ in regex ?

Thanks

Answer 1

[\d+] = one digit (0-9) or + character.

\d+ = one or more digits.

Answer 2

You could also do:

if re.search(r'^[789]\d{9}$', x):

letting the regex handle the len(x)==10 part by using explicit lengths instead of unbounded repetitions.

Answer 3

I think a general explanation about [] and + is what you need.

[] will match with a single character specified inside.
Eg: [qwe] will match with q, w or e.

If you want to enter an expression inside [], you need to use it as [^ expression].

+ will match the preceding element one or more times. Eg: qw+e matches qwe, qwwe, qwwwwe, etc...
Note: this is different from * as * matches preceding element zero or more times. i.e. qw*e matches qe as well.

\d matches with numerals. (not just 0-9, but numerals from other language scripts as well.)

Answer 4

I don't know about complexity but this is also works:

if (len(x)==10 and "789"==x[1:4]):