Iterating each character in a string using Python

In C++, I can iterate over an std::string like this:

std::string str = "Hello World!";
for (int i = 0; i < str.length(); ++i)
{ std::cout << str[i] << std::endl;
}

How do I iterate over a string in Python?

0

9 Answers

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

3

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

1

Even easier:

for c in "test": print c

2

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

3

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 u r y a a

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

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.

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.

1

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)

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