Regular Expression: Common string validation

Question

I am doing some basic validation. The flow of the program goes like:

User inputs a string
Clicks SUBMIT

Now I want to make sure the following rules are fulfilled:

No spaces
Must be alphanumeric... no special charatcers! (ie !@#$%^&*)
Must start with a letter
Must be at least 3 characters

How can I do this using python/django regular expressions?

Please Help

did you mean "Must be at least 3 digits" or "Must be at least 3 characters"? — Abhijit
– Abhijit, Commented Dec 2, 2011 at 14:39

eumiro · Accepted Answer · 2011-12-02 14:41:08Z

6

You can do this in Python without regular expressions:

if a.isalnum() and a[0].isalpha() and len(filter(str.isdigit, a)) >= 3:
    ...

If according to @Toomai "3 digits" are "at least 3 characters long", then this is what you need:

if a.isalnum() and a[0].isalpha() and len(a) >= 3:
    ...

edited Dec 2, 2011 at 14:41

answered Dec 2, 2011 at 14:32

eumiro

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3 Comments

Toomai Over a year ago

If the question means "at least 3 characters long" and not "includes at least 3 numbers", then you can get rid of the filter.

eumiro Over a year ago

@Toomai - added the other alternative too.

Zain Khan Over a year ago

@eumiro: what if we have to include '-' and '_' (dash and underscore) to the list, wont a.isalnum() be a hassle?

Abhijit · Accepted Answer · 2011-12-08 08:56:59Z

3

Try this

re.compile("^[A-Za-z]\w{2,}$")

>>> re.compile("^[A-Za-z]\w{2,}$")
<_sre.SRE_Pattern object at 0x0272C158>
>>> expr=re.compile("^[A-Za-z]\w{2,}$")
>>> expr.match("A12345")
<_sre.SRE_Match object at 0x02721288>
>>> expr.match("A1")
>>> expr.match("1AS")
>>> expr.match("AB1")
<_sre.SRE_Match object at 0x0272E138>
>>> expr.match("ab1")
<_sre.SRE_Match object at 0x02721288>
>>> expr.match("Abhijit$%^&#@")
>>>

edited Dec 8, 2011 at 8:56

answered Dec 2, 2011 at 14:37

Abhijit

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5 Comments

Zain Khan Over a year ago

this does not handle the case for special characters

Zain Khan Over a year ago

example "Abhijit@#%" is true. As point 2 says no special characters except for dash ('-') and underscore ('_')

Abhijit Over a year ago

Sry about that. Just add a $ at the end like re.compile("^[A-Za-z]\w{2,}$")

Abhijit Over a year ago

I have modified my post accordingly

Abhijit Over a year ago

let us continue this discussion in chat

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