How to detect lowercase letters in Python?

问题

I need to know if there is a function that detects the lowercase letters in a string. Say I started writing this program:

s = input('Type a word')

Would there be a function that lets me detect a lowercase letter within the string s? Possibly ending up with assigning those letters to a different variable, or just printing the lowercase letters or number of lowercase letters.

While those would be what I would like to do with it I'm most interested in how to detect the presence of lowercase letters. The simplest methods would be welcome, I am only in an introductory python course so my teacher wouldn't want to see complex solutions when I take my midterm. Thanks for the help!

回答1:

To check if a character is lower case, use the islower method of str. This simple imperative program prints all the lowercase letters in your string:

for c in s:
    if c.islower():
         print c

Note that in Python 3 you should use print(c) instead of print c.

Possibly ending up with assigning those letters to a different variable.

To do this I would suggest using a list comprehension, though you may not have covered this yet in your course:

>>> s = 'abCd'
>>> lowercase_letters = [c for c in s if c.islower()]
>>> print lowercase_letters
['a', 'b', 'd']

Or to get a string you can use ''.join with a generator:

>>> lowercase_letters = ''.join(c for c in s if c.islower())
>>> print lowercase_letters
'abd'

回答2:

You can use built-in function any and generator.

>>> any(c.islower() for c in 'Word')
True

>>> any(c.islower() for c in 'WORD')
False

回答3:

There are 2 different ways you can look for lowercase characters:

Use str.islower() to find lowercase characters. Combined with a list comprehension, you can gather all lowercase letters:
```
lowercase = [c for c in s if c.islower()]
```

You could use a regular expression:

import re

lc = re.compile('[a-z]+')
lowercase = lc.findall(s)

The first method returns a list of individual characters, the second returns a list of character groups:

>>> import re
>>> lc = re.compile('[a-z]+')
>>> lc.findall('AbcDeif')
['bc', 'eif']

回答4:

There are many methods to this, here are some of them:

Using the predefined str method islower():
```
>>> c = 'a'
>>> c.islower()
True
```
Using the ord() function to check whether the ASCII code of the letter is in the range of the ASCII codes of the lowercase characters:
```
>>> c = 'a'
>>> ord(c) in range(97, 123)
True
```
Checking if the letter is equal to it's lowercase form:
```
>>> c = 'a'
>>> c.lower() == c
True
```

Checking if the letter is in the list ascii_lowercase of the string module:

>>> from string import ascii_lowercase
>>> c = 'a'
>>> c in ascii_lowercase
True

But that may not be all, you can find your own ways if you don't like these ones: D.

Finally, let's start detecting:

d = str(input('enter a string : '))
lowers = [c for c in d if c.islower()]

# here i used islower() because it's the shortest and most-reliable
# one (being a predefined function), using this list comprehension
# is (probably) the most efficient way of doing this

回答5:

You should use raw_input to take a string input. then use islower method of str object.

s = raw_input('Type a word')
l = []
for c in s.strip():
    if c.islower():
        print c
        l.append(c)
print 'Total number of lowercase letters: %d'%(len(l) + 1)

Just do -

dir(s)

and you will find islower and other attributes of str

回答6:

import re
s = raw_input('Type a word: ')
slower=''.join(re.findall(r'[a-z]',s))
supper=''.join(re.findall(r'[A-Z]',s))
print slower, supper

Prints:

Type a word: A Title of a Book
itleofaook ATB

Or you can use a list comprehension / generator expression:

slower=''.join(c for c in s if c.islower())
supper=''.join(c for c in s if c.isupper())
print slower, supper

Prints:

Type a word: A Title of a Book
itleofaook ATB

来源：https://stackoverflow.com/questions/12934997/how-to-detect-lowercase-letters-in-python

标签

python

string

lowercase

letters