String datatype and string operations
Python supports many simple and compound datatypes.
Few data types like list, dictionary are mutable and others like string datatype, tuple are immutable.
Mutable datatypes means changes can be done and are reflected in same variable.
Immutable datatypes means changes can be done but not in same variable.
String is collection or sequence of characters.
An empty string represents zero character or we can call it as null string.
A string datatype can be defined with use of single or double quotes.
No separate character type is required instead we can have string of length 1.
String datatype is Immutable
As we know immutable data type indicates datatypes which are non editable or unchangeable in same variable name.
We cannot modify existing string and so strings are immutable datatype.
We can create a new string with reference to existing or orignal string .
Strings are immutable - Justified
If we try to change or assign any new value using [ ] operator in existing string, we get an error message.
Example:
>>> itv='Welcome to itvoyagers'
>>> itv[11]='I'
Traceback (most recent call last):
File "<pyshell#2>", line 1, in <module>
itv[11]='I'
TypeError: 'str' object does not support item assignment
>>>
This TypeError: ‘str’ object does not support item assignment proves that we cannot modify our existing string.
In our case itv holds original string and itv[11]=’I’ tries to edit original string at position 11 with I
As we receive above message, it becomes that string datatype cannot update original value and strings are immutable.
How to deal with immutable string?
To remove TypeError while updating string, we can create a new string based on existing string.
Example:
>>> itv='Welcome to itvoyagers'
>>> new_itv=itv[:11] + 'I' + itv[12:]
>>> new_itv
'Welcome to Itvoyagers'
>>> new_itv1='Hello'+' ' + itv[11:]
>>> new_itv1
'Hello itvoyagers'
This example tells us about how to update a string with new variable.
In this example concatenation of string slicing is done with string.
According to the location of character which we wish to update we can slice the string and concatenate with required update
How to search in a string?
We can search a string or letter from a string.
Following example will help us for better understanding :
Example:
def search_a_string(word,letter):
for i in range(len(word)):
if word[i]==letter:
print("match found")
break
else:
print("match not found")
Output:
>>> search_a_string("itvoyagers","L")
match not found
>>> search_a_string("itvoyagers","v")
match found
>>>
This example indicates that while searching a letter or character case sensitivity must be considered.
Looping and counting on string
We can use loops for counting or traversing a string.
Following example will help us for better understanding :
Example:
#Script to calculate number of times i exists in itvoyagers.in
itv='itvoyagers.in'
counter = 0
for letter in itv:
if letter =='i':
counter+=1
print("Count of i in itvoyagers.in is ", counter)
Output:
>>>
Count of i in itvoyagers.in is 2
This example indicates that by using loops and counter we can easily find count of letters present in particular string.
String Operations
Python supports various string operations which helps in performing tasks easily.
Various string operations include concatenation, repetition, in operator, not in operator, range and slice operators.
Some of the string operations are explained below:
List of string operations in python
- + : Concatenation operator
- This operator is used to join or merge two strings together, i.e. values to the either side of + operator will be merged or concatenated.
-
>>> s="python"
>>> s1="programming"
>>> s+s1
'pythonprogramming'
>>> s+" "+s1
'python programming'
- * : Repetition operator
- This operator creates new string by creating copies of same string.
- This operator here does not multiply number with string but it creates copies of string as per specified number.
-
>>> s="python "
>>> s*3
'python python python '
- [] : Slice operator
- This operator is used to get a character from the given string by specifying the index position in [].
-
>>> s='python programming'
>>> s[6]
' '
>>> s[12]
'a'
>>> s[13]
'm'
- [:] : Range Slice operator
- This operator is used to slice a string by specifying start and end position and also an optional parameter of step value.
-
>>> s='python programming'
>>> s[6:14]
' program'
>>> s[4:14]
'on program'
>>> s[4:14:2]
'o rga'
>>> s[14:4:-2]
'magr '
- in : Membership operator (in)
- This operator will return True is character is present in given string and False otherwise.
-
>>> s='python programming'
>>> 'n' in s
True
>>> 'N' in s
False
- not in : Membership operator(not in)
- This operator will return True is character is not present in given string and False otherwise.
-
>>> s='python programming'
>>> 'n' not in s
False
>>> 'N' not in s
True
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