How can I check if a string only contains letters in Python?

问题

I\'m trying to check if a string only contains letters, not digits or symbols.

For example:

>>> only_letters(\"hello\")
True
>>> only_letters(\"he7lo\")
False

回答1:

Simple:

if string.isalpha():
    print("It's all letters")

str.isalpha() is only true if all characters in the string are letters:

Return true if all characters in the string are alphabetic and there is at least one character, false otherwise.

Demo:

>>> 'hello'.isalpha()
True
>>> '42hello'.isalpha()
False
>>> 'hel lo'.isalpha()
False

回答2:

The str.isalpha() function works. ie.

if my_string.isalpha():
    print('it is letters')

回答3:

For people finding this question via Google who might want to know if a string contains only a subset of all letters, I recommend using regexes:

import re

def only_letters(tested_string):
    match = re.match("^[ABCDEFGHJKLM]*$", tested_string)
    return match is not None

回答4:

The string.isalpha() function will work for you.

See http://www.tutorialspoint.com/python/string_isalpha.htm

回答5:

Looks like people are saying to use str.isalpha.

This is the one line function to check if all characters are letters.

def only_letters(string):
    return all(letter.isalpha() for letter in string)

all accepts an iterable of booleans, and returns True iff all of the booleans are True.

More generally, all returns True if the objects in your iterable would be considered True. These would be considered False

0
None
Empty data structures (ie: len(list) == 0)
False. (duh)

回答6:

Actually, we're now in globalized world of 21st century and people no longer communicate using ASCII only so when anwering question about "is it letters only" you need to take into account letters from non-ASCII alphabets as well. Python has a pretty cool unicodedata library which among other things allows categorization of Unicode characters:

unicodedata.category('陳')
'Lo'

unicodedata.category('A')
'Lu'

unicodedata.category('1')
'Nd'

unicodedata.category('a')
'Ll'

The categories and their abbreviations are defined in the Unicode standard. From here you can quite easily you can come up with a function like this:

def only_letters(s):
    for c in s:
        cat = unicodedata.category(c)
        if cat not in ('Ll','Lu','Lo'):
            return False
    return True

And then:

only_letters('Bzdrężyło')
True

only_letters('He7lo')
False

As you can see the whitelisted categories can be quite easily controlled by the tuple inside the function. See this article for a more detailed discussion.

回答7:

(1) Use str.isalpha() when you print the string.

(2) Please check below program for your reference:-

 str = "this";  # No space & digit in this string
 print str.isalpha() # it gives return True

 str = "this is 2";
 print str.isalpha() # it gives return False

Note:- I checked above example in Ubuntu.

回答8:

You can leverage regular expressions.

>>> import re
>>> pattern = re.compile("^[a-zA-Z]+$")
>>> pattern.match("hello")
<_sre.SRE_Match object; span=(0, 5), match='hello'>
>>> pattern.match("hel7lo")
>>>

The match() method will return a Match object if a match is found. Otherwise it will return None.

An easier approach is to use the .isalpha() method

>>> "Hello".isalpha()
True
>>> "Hel7lo".isalpha()
False

isalpha() returns true if there is at least 1 character in the string and if all the characters in the string are alphabets.

回答9:

A pretty simple solution I came up with: (Python 3)

def only_letters(tested_string):
    for letter in tested_string:
        if letter not in "abcdefghijklmnopqrstuvwxyz":
            return False
    return True

You can add a space in the string you are checking against if you want spaces to be allowed.

来源：https://stackoverflow.com/questions/18667410/how-can-i-check-if-a-string-only-contains-letters-in-python

标签

python

string

conditional-statements