Check if a string contains a number

Question

Most of the questions I\'ve found are biased on the fact they\'re looking for letters in their numbers, whereas I\'m looking for numbers in what I\'d like to be a numberless

Answer 1

You can accomplish this as follows:

if a_string.isdigit(): do_this() else: do_that()

https://docs.python.org/2/library/stdtypes.html#str.isdigit

Using .isdigit() also means not having to resort to exception handling (try/except) in cases where you need to use list comprehension (try/except is not possible inside a list comprehension).

Answer 2

You can use NLTK method for it.

This will find both '1' and 'One' in the text:

import nltk 

def existence_of_numeric_data(text):
    text=nltk.word_tokenize(text)
    pos = nltk.pos_tag(text)
    count = 0
    for i in range(len(pos)):
        word , pos_tag = pos[i]
        if pos_tag == 'CD':
            return True
    return False

existence_of_numeric_data('We are going out. Just five you and me.')

Answer 3

I'm surprised that no-one mentionned this combination of any and map:

def contains_digit(s):
    isdigit = str.isdigit
    return any(map(isdigit,s))

in python 3 it's probably the fastest there (except maybe for regexes) is because it doesn't contain any loop (and aliasing the function avoids looking it up in str).

Don't use that in python 2 as map returns a list, which breaks any short-circuiting

Answer 4

What about this one?

import string

def containsNumber(line):
    res = False
    try:
        for val in line.split():
            if (float(val.strip(string.punctuation))):
                res = True
                break
    except ValueError:
        pass
    return res

containsNumber('234.12 a22') # returns True
containsNumber('234.12L a22') # returns False
containsNumber('234.12, a22') # returns True

Answer 5

This probably isn't the best approach in Python, but as a Haskeller this lambda/map approach made perfect sense to me and is very short:

anydigit = lambda x: any(map(str.isdigit, x))

Doesn't need to be named of course. Named it could be used like anydigit("abc123"), which feels like what I was looking for!

Answer 6

You could apply the function isdigit() on every character in the String. Or you could use regular expressions.

Also I found How do I find one number in a string in Python? with very suitable ways to return numbers. The solution below is from the answer in that question.

number = re.search(r'\d+', yourString).group()

Alternatively:

number = filter(str.isdigit, yourString)

For further Information take a look at the regex docu: http://docs.python.org/2/library/re.html

Edit: This Returns the actual numbers, not a boolean value, so the answers above are more correct for your case

The first method will return the first digit and subsequent consecutive digits. Thus 1.56 will be returned as 1. 10,000 will be returned as 10. 0207-100-1000 will be returned as 0207.

The second method does not work.

To extract all digits, dots and commas, and not lose non-consecutive digits, use:

re.sub('[^\d.,]' , '', yourString)