查找给定字符串是否是python中的单词，字符或数字

Question

Given this string

random_string= '4'

i want to determine if its an integer, a character or just a word i though i could do this

test = int(random_string)
isinstance(test,int) == True

but i realized if the random_string does not contain a number i will have an error

basically the random_string can be of the forms

random_string ='hello'
random_string ='H'
random_string ='r'
random_string ='56'

anyone know a way to do this, kind of confused, for determine is its a character what i did was

chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
random_string in chars == True

i did another string to check if it was a lowercase letter. also to check if its a word, i took the length of the string, if the length is more than one i determine that it is a word or a number

issue is how can i check if its a word or a number

please help

Answer 1

Strings have methods isalpha and isdigit to test if they consist of letters and digits, respectively:

>>> 'hello'.isalpha()
True
>>> '123'.isdigit()
True

Note that they only check for those characters, so a string with spaces or anything else will return false for both:

>>> 'hi there'.isalpha()
False

However, if you want the value as a number, you're better off just using int . Note that there's no point checking with isinstance whether the result is indeed an integer. If int(blah) succeeds, it will always return an integer; if the string doesn't represent an integer, it will raise an exception.

Answer 2

Take your pick.

>>> '4'.isdigit()
True
>>> '-4'.isdigit()
False
>>> int('-4')
-4
>>> 'foo'.isdigit()
False
>>> int('foo')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: 'foo'

Answer 3

To implement the logic your asking for, I guess the most pythonic way would be to use exception handling:

try:
  n = int(random_string)
except ValueError: 
  if len(random_string) > 1:
    # it's a word
  else:
    # it's a character (or the empty string)

To check the case, you can use the string method islower() .

Answer 4

To gain more control, esp in case if you have some type of strings which inbuilt functions don't support, you can use re -

A regular exp like below to check if its a number -

re.findall(r'^[-]?[0-9]*[\.]?[0-9]*$', s)

and the following regular exp to check if its a string -

r'^[a-zA-Z]+$'

Please note that this is just for demo, you should modify the regular exp as per your needs.