3) Python String
3.1) String
Concatenation
a =
"Hello"
b =
"World"
c = a + "
" + b
print(c)
Output:
Hello World
3.2) User Input
Python provide two inbuilt functions to read input from
the keyboard:
- raw_input(
prompt ) -- Used in Python v2
- input(
prompt ) -- Used in Python v3
Note: Whatever you enter as input is converted into
a string. If you enter an integer value, the input() function still
converts it into a string - you need to explicitly convert it into an integer
in your code using typecasting.
Name =
input("Type Your name :")
To take two or more inputs in one input line, we can use
the split()
function.
name, age =
input("enter your name and age :".split()
print(name)
print(age)
Output:
enter your name
and age:Bob 27
Bob
27
split()
- separates by spaces
split(",")
- separates by comma
3.3) int() and str()
function
The int()
function converts the specified value into an integer number.
The str()
function converts the specified value into a string.
Example:
first_number =
int(input("Enter first number "))
second_number = int(input("Enter
second number "))
Total =
first_number + second_number
print("Total
is " + str(Total))
Image: 7 + 7 = 14
3.4) String Formatting
Example using format() and place holder {}.
name =
"James"
age = 33
print("Hello
" + name + " your age is " + str(age)) # Ugly format
print("Hello
{} your age is {}".format(name,age)) # Looks better
Image: Using Python format()
3.5) String Indexing
The index()
method
- finds the first occurrence of the specified value
- raises an exception if the value is not found
- is almost the same as the find() method (the find()
method returns -1 if the value is not found)
Syntax:
str.index(str, beg = 0 end = len(string))
Parameters:
str - specifies the string to be searched
beg - (optional) is the starting index (default is
0)
end - (optional) is the ending index (default
equal to the length of the string)
Examples:
txt =
"Hello, welcome to my world."
x =
txt.index("welcome")
y =
txt.index("e", 5 , 10)
print(x)
print(y)
print(txt.find("q"))
print(txt.index("q"))
Output:
7
8
-1
Traceback
(most recent call last):
File "main.py", line 7, in
<module>
print(txt.index("q"))
ValueError:
substring not found
Print the Value of any Particular Postion
#print 5th
postion (counts from 0)
language =
"Python"
print(language[4])
#result is o
#print last
position
print(language[-1])
#result is n
3.6) String Slicing and
Step Argument
String Slicing Syntax:
String[Start argument : Stop Argument -1]
Example - get
characters from position 2 to position 5 (not included):
aString =
"Hello World!"
print(aString[2:5])
Output:
llo
String Slicing
with Stop Argument Syntax:
String[Start argument : Stop Argument -1 : step]
Example - display
string from 0 to 11 by taking 2 steps:
aString =
"Hello World!"
print(aString[0:11:2])
Output:
HloWrd
3.7) Basic String
Methods
Python has a set of built-in methods that you can apply
to strings.
len() function -
gives the length of the string including spaces
lower() method -
gives the string in lower case
upper() method -
gives the string in upper case
title() method -
capitalizes the 1st letter of the string
count() method -
count of occurrences of a particular selected character
Examples:
name =
"nIGel mANSell"
print(len(name))
print(name.lower())
print(name.upper())
print(name.title())
print(name.count("l"))
Output:
13
nigel Mansell
NIGEL MANSELL
Nigel Mansell
3
lstrip() method - returns
a left trim version of the string
Syntax:
string.lstrip(characters)
Note: Space is the
default leading character to remove.
Example 1:
txt = " banana"
print("of
all fruits", txt.lstrip(), "is my favourite")
Output 1:
of all fruits
banana is my favourite
Example 2:
txt =
",,,rraaww...banana"
print(txt.lstrip(",.raw"))
Output 2:
banana
find() method finds
the first occurrence of the specified value, and returns -1 if the value is not
found
Syntax:
string.find(value, start, end)
Example:
######
012345678901
print("Hello
and welcome to my world".find("e", 5, 15))
Output:
11
replace() method
replaces a specified phrase with another specified phrase
Syntax:
string.replace(oldvalue,newvalue,count)
Example:
# ..... 1 . 2
............................... 3 .....
print("one
one was a race horse, two two was one too".replace("one",
"three", 2))
Output:
three three was a
race horse, two two was one too
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