# Day 5: Strings¶

## 1. Strings¶

String is one the basic datatypes of the python language. There are many ways to define a string but we use the most common method by writing a sentence or paragraph inside single(') or double(") quotes.

mystring = "python is awesome"
mystring = 'python is awesome'
print(mystring)

python is awesome


Warning

Even numbers in single or double quotes behaves as an string.

temp = "38.7"
print(type(temp))

<class 'str'>


### 1.1 Accessing data inside list¶

String behaves very much similar to the list. You can think that it is a list where each character has as index. We can obtain a character from its position or index. As counting starts in python from 0, So the first index is 0 and second index is 1 and so on.

mystring = "python is awesome"
fifth = mystring[4] # fifth character from start
last_fifth = mystring[-4] # fifth character from last
print(fifth, last_fifth)

o s


### 1.2 Basic list operations¶

• Length: The length of a string can be computed as follows

print(len(mystring))

17

• Addition: Two or more string can be added with + operation as follows

a = "Sandeep "
b = "Suman"
c = a + b
print(c)

Sandeep Suman

• Multiplication: Repetition can be achieved with * operation as follows

a = 'Hi!' * 5
print(a)

Hi!Hi!Hi!Hi!Hi!

• Slicing: A part of of string starting with i index and end before j can be obtained by List[i:j], for example

c = "sandeep"
print(c[1:4]) # start from 1st and end before 4th (counting starts with 0)
print(c[4:])  # everything after 4th (counting starts with 0)
print(c[:4]) # to get the substring from start and end before 4th (counting starts with 0)

and
eep
sand

• Extended Slicing: The slicing in string is more flexible as it accepts more than two arguments. For example X[1:10:2] will get every other item in the substring X[1:10]

univ = "TilkaManjhiBhagalpurUniversity"
s1 = univ[1:20:2] # get even position elements in substring univ[1:20]
s2 = univ[::2]  # get even position elements
s3 = univ[::-1] # reverse the string
print(s)

ikMnhBaapr
TlaajihgluUiest
ytisrevinUruplagahBihjnaMakliT


### 1.3 String Methods¶

Some of the string method is the following

• Capitalize: This method is used make first letter capital.

msg = "Welcome to FaculTy DevelopMent prograMME."
print(msg.capitalize())

Welcome to faculty development programme.

• Lower: It will make every letter small.

msg = "Welcome to FaculTy DevelopMent prograMME."
print(msg.lower())

welcome to faculty development programme.

• Replace: It will one substring with another.

msg = "Welcome to FaculTy DevelopMent prograMME."
print(msg.replace("M", "X")) # replace all M with X

Welcome to FaculTy DevelopXent prograXXE.


To replace only one instance, we can pass one more argument.

msg = "Welcome to FaculTy DevelopMent prograMME."
print(msg.replace("M", "X", 1)) # replace the first M with X

Welcome to FaculTy DevelopXent prograMME.

• Find: It will find one string in another string.

msg = "Welcome to FaculTy DevelopMent prograMME."
print(msg.find("to")) # finds the position of "to"

8


You can think of this as the following

msg = "Welcome to FaculTy DevelopMent prograMME."
position = msg.find("to") # position of to
original = msg[:8] + "to" + msg[8+2:] # the original msg

print(original)

Welcome to FaculTy DevelopMent prograMME.

• Split: The split method will convert a string to list of substring

msg = "Welcome to FaculTy DevelopMent prograMME."
L = msg.split() # default method will split at each whitespace
print(L)

['Welcome', 'to', 'FaculTy', 'DevelopMent', 'prograMME.']


The split method is much more flexible. We can pass an argument to tell about the marker for split.

msg = "Amar,Akbar,Anthony"
L = msg.split(",") # split each part with ","
print(L)

['Amar', 'Akbar', 'Anthony']

• Join: The join method works opposite of split. We can make a string using the split method.

L = ['Amar', 'Akbar', 'Anthony']
msg = " ".join(L) # the string in between will go before "."
print(msg)

Amar Akbar Anthony


If we want to join with , in all the elements of the list.

L = ['Amar', 'Akbar', 'Anthony']
msg = ",".join(L)
print(msg)

Amar,Akbar,Anthony


Ex: Try to join the list L with comma and space. Ex: Try to join in smaller latter.

Tip

There are huge number of list methods in python, and python programming is considered to be very powerful in list manipulation. You can google search to do any kind of list manipulation.

### 1.4 Membership and Iterating a String¶

• Membership tells if a string is a part of larger string or not.

print("T" in "TMBU")
print("math" in "mathematics")
print("ss" in "sandeep")

True
True
False

• The iteration in string work similar to list as follows

univ = "TMBU"
for i in univ:
print(i)

T
M
B
U


Ex: Write a program to check if the word 'orange' is present in the "This is orange juice".

Ex: Convert the date written in the format "10/06/2020" to "10-06-2020".

Ex: Convert "Tilka MaJHi BHaGalPUR UNIVersiTy" to "Tilka Manjhi Bhagalpur University".