Python: Comparing string variable against multiple sub-strings

Question

I am new to Python and trying to learn python from Perl. In Perl, if I want to compare a string against multiple sub-strings, I would use the following:

sub matchCity {
    my $cityName = shift;
    print "$cityName is a valid city name\n" if ($cityName =~ /kyo|par|omba/);
}

matchCity('tokyo'); # tokyo is a valid city name
matchCity('paris'); # paris is a valid city name
matchCity('bombay'); # bombay is a valid city name
matchCity('chicago'); # Doesn't print anything

How can I do this in python?

WHAT'S WRONG WITH CHICAGO!?!

Nick T
– Nick T

2013-10-29 00:53:45 +00:00
Commented Oct 29, 2013 at 0:53 — Nick T
– Nick T, Commented Oct 29, 2013 at 0:53

arshajii · Accepted Answer · 2013-10-29 00:23:30Z

3

You don't actually need regex for this:

>>> def matchCity(s):
...     if any(r in s for r in ('kyo','par','omba')):
...         print s, 'is a valid city name'
... 
>>> matchCity('tokyo')
tokyo is a valid city name
>>> matchCity('paris')
paris is a valid city name
>>> matchCity('bombay')
bombay is a valid city name
>>> matchCity('chicago')  # doesn't print anything
>>>

answered Oct 29, 2013 at 0:23

arshajii

130k26 gold badges246 silver badges293 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

SethMMorton Over a year ago

Don't all of them return None?

Corley Brigman Over a year ago

if i replace the print with a simple statement (i used x=1) to get valid timings, this appears to be about twice fast as the re method (1.15 uS vs. 2.01uS on my machine).

arshajii Over a year ago

@CorleyBrigman I'm not at all surprised. The re approach does a lot of work behind the scenes (parsing the regular expression etc.).

ikegami · Accepted Answer · 2013-10-29 02:33:56Z

2

import re

def matchCity(city_name):
    if re.search('kyo|par|omba', city_name):
        print "{} is a valid city name".format(city_name)

matchCity('tokyo') # tokyo is a valid city name
matchCity('paris') # paris is a valid city name
matchCity('bombay') # bombay is a valid city name
matchCity('chicago') # Doesn't print anything

edited Oct 29, 2013 at 2:33

ikegami

391k17 gold badges291 silver badges554 bronze badges

answered Oct 29, 2013 at 0:22

John La Rooy

306k54 gold badges378 silver badges513 bronze badges

6 Comments

SethMMorton Over a year ago

Don't all of them return None?

John La Rooy Over a year ago

The function returns None. Is that what you mean?

SethMMorton Over a year ago

Yes. In the comments you added, you annotate that when 'chicago' is passed, it returns undef. I was saying that a) shouldn't that be None, and b) since all of them return None, the return value can't be checked to see if the city matches or not (since I assume that's why it was mentioned that it returns undef).

dawg Over a year ago

Seth is right here: With Perl, a subroutine returns the value of the last calculation unless there is an explicit return value. Python returns None unless there is an explicit return value.

John La Rooy Over a year ago

Ah, ok, I copied those lines verbatim from the question

|

LeartS · Accepted Answer · 2013-10-29 00:29:12Z

0

With regular expressions:

import re
city = re.compile('kyo|par|omba', re.I)
matchCity = lambda x: city.search(x)

And you can use matchCity("example_city") as condition:

if matchCity("tokyo"):   print "Valid city!" # Valid city!
if matchCity("paris"):   print "Valid city!" # Valid city!
if matchCity("bombay"):  print "Valid city!" # Valid city!
if matchCity("chicago"): print "Valid city!" #

answered Oct 29, 2013 at 0:29

LeartS

2,9162 gold badges27 silver badges46 bronze badges

Comments

Matimus · Accepted Answer · 2013-10-29 00:32:26Z

0

Python has regular expressions. So you could do this:

import re

city_names = re.compile(r'kyo|par|omba')

def match_city(city_name):
    if city_names.search(city_name):
        print city_name, "is a valid city name"

Normally I would tell you to avoid regular expressions if you can. But matching one of multiple sub-strings is actually a case where they likely perform better than a loop. This is especially true as the number of sub-strings grows.

answered Oct 29, 2013 at 0:32

Matimus

5222 silver badges8 bronze badges

2 Comments

SethMMorton Over a year ago

According to the comments on @arshajii's post, re is slower than string methods even in this case.

Corley Brigman Over a year ago

but he might be right... the test i did includes the compile of the regex, and if you have more substrings to check, the timing advantage might shift. will try it later.

Collectives™ on Stack Overflow

Python: Comparing string variable against multiple sub-strings

4 Answers 4

3 Comments

6 Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

6 Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related