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

Solution 1

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

\d+ = one or more digits.

Solution 2

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.)

Solution 3

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.

Comments

[Sebastian Proske]

[\d]+ would have been correct, [\d+] means one charatcer thats either a number or a plus. Also remove the |s from the character class, as they are treated as just literal |

[Barmar]

I think you need to read a regexp tutorial. You seem to be using [] where you really want ().

[Jithin Pavithran]

[] looks for a single character inside. Eg: [abc] look for a, b or c.

[Barmar]

Escape sequences work inside [], so it's a digit or +.