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

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.

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".

2. References¶

1. W3School on String