Reject optional whitespaces after area code and before local number (US)

I have a regex that parses US phone numbers into 3 strings.

import re
s = '  916-2221111 ' # this also works'[phone]   '

reg_ph = re.match(r'^s*(?(d{3}))?-? *(d{3})-? *-?(d{4})', s)
if reg_ph:
    return reg_ph.groups()

else:
    raise ValueError ('not a valid phone number')

it works perfectly on the numbers:

'[phone]   '
'  916-2221111 '

Now I need to add an additional regex to generate a Value Error for numbers such as

s = '916 111-2222' # there are white spaces between the area code and a local number and NO ')'

I tried

reg_ph = re.match(r'^s*(?(d{3}))?s*-? *(d{3})-? *-?(d{4})', s)
reg_ph = re.match(r'^s*(?(d{3}))?s*-? *(d{3})-? *-?(d{4})', s)

but non rejects the string in question

I will greatly appreciate any ideas. I am very new to Regex!

Answer

In Python re you could use a conditional to check for group 1 having the opening parenthesis.

If that is the case match the closing parenthesis, optional spaces and 3 digits. Else match - and 3 digits.

If you use re.match you can omit ^

^s*(()?d+(?(1))s*d{3}|-d{3})-?d{4}

If you want to match the whole string and trailing whitespace chars:

^s*(()?d+(?(1))s*d{3}|-d{3})-?d{4}s*$

In parts, the pattern matches:

• ^ Start of string
• s* Match optional whitespace chars
• (()? Optional group 1, match (
• d+ Match 1+ digits
• (? Conditional
  • (1))s*d{3} If group 1 exist, match the closing ), optional whitespace chars and 3 digits
  • | Or
  • -? Match optional –
  • d{3} Match 3 digits
• ) close conditional
• -?d{4} Match optional – and 4 digits

See a regex demo

For example, using capture groups in the pattern to get the digits:

import re

strings = [' [phone]',' 916-2221111 ', '916 111-2222']
pattern =r's*(()?(d+)(?(1))s*(d{3})|-(d{3}))-?(d{4})s*$'

for item in strings:
  m=re.match(pattern, item)
  if m:
    t = tuple(s for s in m.groups() if s is not None and s.isdigit())
    print(t)
  else:
    print("no match for " + item)

Output

('916', '111', '2222')
('916', '222', '1111')
no match for 916 111-2222

Python demo