How do I get a substring of a string in Python?

Question

Is there a way to substring a string in Python, to get a new string from the third character to the end of the string?

Maybe like myString[2:end]?

If leaving the second part means 'till the end', and if you leave the first part, does it start from the start?

Answer 1

>>> x = "Hello World!"
>>> x[2:]
'llo World!'
>>> x[:2]
'He'
>>> x[:-2]
'Hello Worl'
>>> x[-2:]
'd!'
>>> x[2:-2]
'llo Worl'

Python calls this concept "slicing" and it works on more than just strings. Take a look here for a comprehensive introduction.

Answer 2

Just for completeness as nobody else has mentioned it. The third parameter to an array slice is a step. So reversing a string is as simple as:

some_string[::-1]

Or selecting alternate characters would be:

"H-e-l-l-o- -W-o-r-l-d"[::2] # outputs "Hello World"

The ability to step forwards and backwards through the string maintains consistency with being able to array slice from the start or end.

Answer 3

Substr() normally (i.e. PHP and Perl) works this way:

s = Substr(s, beginning, LENGTH)

So the parameters are beginning and LENGTH.

But Python's behaviour is different; it expects beginning and one after END (!). This is difficult to spot by beginners. So the correct replacement for Substr(s, beginning, LENGTH) is

s = s[ beginning : beginning + LENGTH]

Answer 4

A common way to achieve this is by string slicing.

MyString[a:b] gives you a substring from index a to (b - 1).

Answer 5

One example seems to be missing here: full (shallow) copy.

>>> x = "Hello World!"
>>> x
'Hello World!'
>>> x[:]
'Hello World!'
>>> x==x[:]
True
>>>

This is a common idiom for creating a copy of sequence types (not of interned strings), [:]. Shallow copies a list, see Python list slice syntax used for no obvious reason.

Answer 6

Is there a way to substring a string in Python, to get a new string from the 3rd character to the end of the string?

Maybe like myString[2:end]?

Yes, this actually works if you assign, or bind, the name,end, to constant singleton, None:

>>> end = None
>>> myString = '1234567890'
>>> myString[2:end]
'34567890'

Slice notation has 3 important arguments:

• start
• stop
• step

Their defaults when not given are None - but we can pass them explicitly:

>>> stop = step = None
>>> start = 2
>>> myString[start:stop:step]
'34567890'

If leaving the second part means 'till the end', if you leave the first part, does it start from the start?

Yes, for example:

>>> start = None
>>> stop = 2
>>> myString[start:stop:step]
'12'

Note that we include start in the slice, but we only go up to, and not including, stop.

When step is None, by default the slice uses 1 for the step. If you step with a negative integer, Python is smart enough to go from the end to the beginning.

>>> myString[::-1]
'0987654321'

I explain slice notation in great detail in my answer to Explain slice notation Question.

Answer 7

You've got it right there except for "end". It's called slice notation. Your example should read:

new_sub_string = myString[2:]

If you leave out the second parameter it is implicitly the end of the string.

Answer 8

I would like to add two points to the discussion:

1. You can use None instead on an empty space to specify "from the start" or "to the end":

   'abcde'[2:None] == 'abcde'[2:] == 'cde'
   

   This is particularly helpful in functions, where you can't provide an empty space as an argument:

   def substring(s, start, end):
       """Remove `start` characters from the beginning and `end` 
       characters from the end of string `s`.
   
       Examples
       --------
       >>> substring('abcde', 0, 3)
       'abc'
       >>> substring('abcde', 1, None)
       'bcde'
       """
       return s[start:end]
   

2. Python has slice objects:

   idx = slice(2, None)
   'abcde'[idx] == 'abcde'[2:] == 'cde'
   

Answer 9

If myString contains an account number that begins at offset 6 and has length 9, then you can extract the account number this way: acct = myString[6:][:9].

If the OP accepts that, they might want to try, in an experimental fashion,

myString[2:][:999999]

It works - no error is raised, and no default 'string padding' occurs.

Answer 10

Well, I got a situation where I needed to translate a PHP script to Python, and it had many usages of substr(string, beginning, LENGTH).
If I chose Python's string[beginning:end] I'd have to calculate a lot of end indexes, so the easier way was to use string[beginning:][:length], it saved me a lot of trouble.

Answer 11

Maybe I missed it, but I couldn't find a complete answer on this page to the original question(s) because variables are not further discussed here. So I had to go on searching.

Since I'm not yet allowed to comment, let me add my conclusion here. I'm sure I was not the only one interested in it when accessing this page:

 >>>myString = 'Hello World'
 >>>end = 5

 >>>myString[2:end]
 'llo'

If you leave the first part, you get

 >>>myString[:end]
 'Hello' 

And if you left the : in the middle as well you got the simplest substring, which would be the 5th character (count starting with 0, so it's the blank in this case):

 >>>myString[end]
 ' '

Answer 12

Using hardcoded indexes itself can be a mess.

In order to avoid that, Python offers a built-in object slice().

string = "my company has 1000$ on profit, but I lost 500$ gambling."

If we want to know how many money I got left.

Normal solution:

final = int(string[15:19]) - int(string[43:46])
print(final)
>>>500

Using slices:

EARNINGS = slice(15, 19)
LOSSES = slice(43, 46)
final = int(string[EARNINGS]) - int(string[LOSSES])
print(final)
>>>500

Using slice you gain readability.

Answer 13

a="Helloo"
print(a[:-1])

In the above code, [:-1] declares to print from the starting till the maximum limit-1.

OUTPUT :

>>> Hello

Note: Here a [:-1] is also the same as a [0:-1] and a [0:len(a)-1]

a="I Am Siva"
print(a[2:])

OUTPUT:

>>> Am Siva

In the above code a [2:] declares to print a from index 2 till the last element.

Remember that if you set the maximum limit to print a string, as (x) then it will print the string till (x-1) and also remember that the index of a list or string will always start from 0.

Answer 14

str1='There you are'
>>> str1[:]
'There you are'

>>> str1[1:]
'here you are'

#To print alternate characters skipping one element in between

>>> str1[::2]
'Teeyuae'

#To print last element of last two elements
>>> str1[:-2:-1]
'e'

#Similarly
>>> str1[:-2:-1]
'e'


#Using slice datatype

>>> str1='There you are'
>>> s1=slice(2,6)
>>> str1[s1]
'ere '