How do I get a substring of a string in Python?
PythonStringSubstringPython Problem Overview
I want to get a new string from the third character to the end of the string, e.g. myString[2:end]
. If omitting the second part means 'till the end', and if you omit the first part, does it start from the start?
Python Solutions
Solution 1 - Python
>>> 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.
Solution 2 - Python
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.
Solution 3 - Python
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]
Solution 4 - Python
A common way to achieve this is by string slicing.
MyString[a:b]
gives you a substring from index a to (b - 1).
Solution 5 - Python
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.
Solution 6 - Python
> 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.
Solution 7 - Python
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.
Solution 8 - Python
I would like to add two points to the discussion:
-
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]
-
Python has slice objects:
idx = slice(2, None) 'abcde'[idx] == 'abcde'[2:] == 'cde'
Solution 9 - Python
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.
Solution 10 - Python
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.
Solution 11 - Python
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 '
Solution 12 - Python
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]
' '
Solution 13 - Python
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.
Solution 14 - Python
text = "StackOverflow"
#using python slicing, you can get different subsets of the above string
#reverse of the string
text[::-1] # 'wolfrevOkcatS'
#fist five characters
text[:5] # Stack'
#last five characters
text[-5:] # 'rflow'
#3rd character to the fifth character
text[2:5] # 'rflow'
#characters at even positions
text[1::2] # 'tcOefo'
Solution 15 - Python
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.
Solution 16 - Python
I have a simpler solution using for loop to find a given substring in a string. Let's say we have two string variables,
main_string = "lullaby"
match_string = "ll"
If you want to check whether the given match string exists in the main string, you can do this,
match_string_len = len(match_string)
for index,value in enumerate(main_string):
sub_string = main_string[index:match_string_len+index]
if sub_string == match_string:
print("match string found in main string")