使用 Python 迭代字符串中的每个字符

Question

How can I iterate over a string in Python (get each character from the string, one at a time, each time through a loop)?

Answer 1

As Johannes pointed out,

for c in "string":
    #do something with c

You can iterate pretty much anything in python using the for loop construct,

for example, open("file.txt") returns a file object (and opens the file), iterating over it iterates over lines in that file

with open(filename) as f:
    for line in f:
        # do something with line

If that seems like magic, well it kinda is, but the idea behind it is really simple.

There's a simple iterator protocol that can be applied to any kind of object to make the for loop work on it.

Simply implement an iterator that defines a next() method, and implement an __iter__ method on a class to make it iterable. (the __iter__ of course, should return an iterator object, that is, an object that defines next() )

See official documentation

Answer 2

If you need access to the index as you iterate through the string, use enumerate() :

>>> for i, c in enumerate('test'):
...     print i, c
... 
0 t
1 e
2 s
3 t

Answer 3

Even easier:

for c in "test":
    print c

Answer 4

Just to make a more comprehensive answer, the C way of iterating over a string can apply in Python, if you really wanna force a square peg into a round hole.

i = 0
while i < len(str):
    print str[i]
    i += 1

But then again, why do that when strings are inherently iterable?

for i in str:
    print i

Answer 5

Well you can also do something interesting like this and do your job by using for loop

#suppose you have variable name
name = "Mr.Suryaa"
for index in range ( len ( name ) ):
    print ( name[index] ) #just like c and c++ 

Answer is

M r. S uryaa

However since range() create a list of the values which is sequence thus you can directly use the name

for e in name:
    print(e)

This also produces the same result and also looks better and works with any sequence like list, tuple, and dictionary.

We have used tow Built in Functions ( BIFs in Python Community )

1) range() - range() BIF is used to create indexes Example

for i in range ( 5 ) :
can produce 0 , 1 , 2 , 3 , 4

2) len() - len() BIF is used to find out the length of given string

Answer 6

If you would like to use a more functional approach to iterating over a string (perhaps to transform it somehow), you can split the string into characters, apply a function to each one, then join the resulting list of characters back into a string.

A string is inherently a list of characters, hence 'map' will iterate over the string - as second argument - applying the function - the first argument - to each one.

For example, here I use a simple lambda approach since all I want to do is a trivial modification to the character: here, to increment each character value:

>>> ''.join(map(lambda x: chr(ord(x)+1), "HAL"))
'IBM'

or more generally:

>>> ''.join(map(my_function, my_string))

where my_function takes a char value and returns a char value.

Answer 7

Several answers here use range . xrange is generally better as it returns a generator, rather than a fully-instantiated list. Where memory and or iterables of widely-varying lengths can be an issue, xrange is superior.

Answer 8

You can use formatted string literals ( PEP498 ; Pyton 3.6+) with print and sequence unpacking and enumerate :

print(*(f'{idx} {char}' for idx, char in enumerate('Hello!')), sep='\n')

0 H
1 e
2 l
3 l
4 o
5 !

If printing tuple values are sufficient, there is no need for the generator expression:

print(*enumerate('Hello!'), sep='\n')

(0, 'H')
(1, 'e')
(2, 'l')
(3, 'l')
(4, 'o')
(5, '!')

Answer 9

You can also do the following:

txt = "Hello World!"
print (*txt, sep='\n')

This does not use loops but internally print statement takes care of it.

* unpacks the string into a list and sends it to the print statement

sep='\n' will ensure that the next char is printed on a new line

The output will be:

H
e
l
l
o
 
W
o
r
l
d
!

If you do need a loop statement, then as others have mentioned, you can use a for loop like this:

for x in txt: print (x)

Answer 10

If you ever run in a situation where you need to get the next char of the word using __next__() , remember to create a string_iterator and iterate over it and not the original string (it does not have the __next__() method)

In this example, when I find a char = [ I keep looking into the next word while I don't find ] , so I need to use __next__

here a for loop over the string wouldn't help

myString = "'string' 4 '['RP0', 'LC0']' '[3, 4]' '[3, '4']'"
processedInput = ""
word_iterator = myString.__iter__()
for idx, char in enumerate(word_iterator):
    if char == "'":
        continue

    processedInput+=char

    if char == '[':
        next_char=word_iterator.__next__()
        while(next_char != "]"):
          processedInput+=next_char
          next_char=word_iterator.__next__()
        else:
          processedInput+=next_char