Validate name using Python regex

Question

I want to return true if name is valid. Name can contain:

upper or lower case characters
no numbers or special characters
can be one or two words with a single space in the middle
first name and last name can be between 2-25 characters each

eg.

John Smith = true
John = true
JoHn = true
John Sm1th = false
John $mith = false
J0hn = false
John Smith = false (two spaces between names)

Here is my code thus far. It fails some of these test cases.

import re

if re.findall('[A-Za-z]{2,25}\s[A-Za-z]{2,25}', string):
    print("true")
else:
    print("false")

First, to test a string don't use re.findall but re.match. — Casimir et Hippolyte
– Casimir et Hippolyte, Commented Dec 18, 2017 at 22:13
Don't make us try to guess which test cases fail. It should be part of your question! — erik258
– erik258, Commented Dec 18, 2017 at 22:39

akuiper · Accepted Answer · 2017-12-18 22:18:53Z

5

To match one or two words, you need to make either the first name or the last name optional, also you need anchors to assure it's not partial matching or use re.fullmatch instead of re.findall:

lst = ['John Smith', 'John', 'JoHn', 'John Sm1th', 'John $mith', 'J0hn', 'John  Smith']

import re
[re.fullmatch('[A-Za-z]{2,25}( [A-Za-z]{2,25})?', x) for x in lst]
# [<_sre.SRE_Match object; span=(0, 10), match='John Smith'>, <_sre.SRE_Match object; span=(0, 4), match='John'>, <_sre.SRE_Match object; span=(0, 4), match='JoHn'>, None, None, None, None]

Convert result to bool:

[bool(re.fullmatch('[A-Za-z]{2,25}( [A-Za-z]{2,25})?', x)) for x in lst]
# [True, True, True, False, False, False, False]

answered Dec 18, 2017 at 22:18

akuiper

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5 Comments

albert Over a year ago

Where [A-Za-z] can be shortened as [A-z]

Casimir et Hippolyte Over a year ago

@albert: no it's wrong, look at the ascii table to see all characters between A and z. However, you can use [a-z] with the re.I flag.

akuiper Over a year ago

@albert You actually can't, see this answer.

Woody Pride Over a year ago

is there any practical difference between a regex of " " and "\s"?

akuiper Over a year ago

@WoodyPride \s can match normal white space, tab \t and new line characters \n or \r on windows while " " only matches normal white space.

Nick T · Accepted Answer · 2017-12-18 22:28:56Z

0

'[A-Za-z]{2,25}||\s[A-Za-z]{2,25}' this should work. You can test your regular expressions at https://pythex.org/

edited Dec 18, 2017 at 22:28

Nick T

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answered Dec 18, 2017 at 22:13

Abhishek Ramamurthy

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