List in Python

LIST

• List is an ordered collection and are commonly used to collect  homogeneous objects, but can also contain heterogeneous data.

 #program to define List

 l1 = [10, 20, 30, 40, 50]
 l2 = [10, 10.25, 30.40,"Techno Xpresss"]
 print("l1 : ", l1)
 print("l2 : ", l2)
 print("type(l1) :", type(l2[0]))
 print("type(l2) :", type(l2[1]))

 #output

 l1 :  [10, 20, 30, 40, 50]
 l2 :  [10, 10.25, 30.4, 'Techno Xpresss']
 type(l1) : <class 'int'>
 type(l2) : <class 'float'>

• To define a list, we use [ ] (square brackets), each member is separated by ','

                    Syntax :
                                List_name = [member1, member2,..]

 #program to define List

 l1 = [10, 20, 30, 40, 50]
 print("l1 : ", l1)
 print("type(l1) :", type(l1))

 #output

 l1 :  [10, 20, 30, 40, 50]
 type(l1) : <class 'list'>

• List can be defined as empty List.

 #program to define empty List

 l1 = []
 print("l1 : ", l1)
 print("type(l1) :", type(l1))

 #output

 l1 :  []
 type(l1) : <class 'list'>

• List can be defined with single member

 #program

 l1 = [10]
 print("l1 : ", l1)
 print("type(l1)", type(l1))


 #output
 l1 :  [10]
 type(l1) <class 'list'>

• To access individual element of List, indexing is used.

 #program to call a member of List by index

 l1 = [10, 20, 30, 40, 50]
 print("l1 : ", l1[0])
 print("type(l1[0]) :", type(l1[0]))

 #output

 l1 :  10
 type(l1[0]) : <class 'int'>

• List allows Positive and negative indexing.

 #program tocall member by positive and negative indexing in List

 l1 = [10, 20, 30, 40, 50]

 print("l1[0]  : ", l1[0])
 print("l1[-5] : ", l1[-5])

 print("l1[5]  : ", l1[4])
 print("l1[-1] : ", l1[-1])

 print("l1[2]  : ", l1[2])
 print("l1[-3] : ", l1[-3])


 #output

 l1[0]  :  10
 l1[-5] :  10
 l1[5]  :  50
 l1[-1] :  50
 l1[2]  :  30
 l1[-3] :  30

• List allows multiplication and addition operations.

#program to understand addition and multiplication in List

l1 = [10, 20, 30, 40, 50]
l2 = [10, 10.25, 30.40,"Techno Xpresss"]
print("l1      : ", l1)
print("l2      : ", l2)
print("l1 + l2 : ", l1+l2)      # add 2 list
print("l1 * 2  : ", l1*2)        # multiple list1 with 2
print("l2 * 3  : ", l2*3)        # multiple list2 with 3

#output

l1      :  [10, 20, 30, 40, 50]
l2      :  [10, 10.25, 30.4, 'Techno Xpresss']
l1 + l2 :  [10, 20, 30, 40, 50, 10, 10.25, 30.4, 'Techno Xpresss']
l1 * 2  :  [10, 20, 30, 40, 50, 10, 20, 30, 40, 50]
l2 * 3  :  [10, 10.25, 30.4, 'Techno Xpresss', 10, 10.25, 30.4, 'Techno Xpresss', 10, 10.25, 30.4, 'Techno Xpresss']

adding 2 list, will cascade 2nd list in 1st list.

multiplying list with any number n, resulted list will have original list data n times.

• Limitation:
• we can not add any data to list via addition

 #program to add any value to List

 l1 = [10, 20, 30, 40, 50]
 print("l1 : ", l1)

 print("l1 + 60 : ", l1 + 60)

 #output

 l1 :  [10, 20, 30, 40, 50]
 Traceback (most recent call last):
   File "C:/Self_Practice_Er_M_S_Dandyan/Python/Pycharm/xml/main.py", line 68, in <module>
     print("l1 + 60 : ", l1 + 60)
 TypeError: can only concatenate list (not "int") to list

• we can not multiply 2 list with each other

 #program to try multiplying 2 List

 l1 = [10, 20, 30, 40, 50]
 l2 = [10, 20, 30]
 print("l1 : ", l1)
 print("l2 : ", l2)
 print("l1 * l2 : ", l1*l2)

 #output

 l1 :  [10, 20, 30, 40, 50]
 l2 :  [10, 20, 30]
 Traceback (most recent call last):
   File "C:/Self_Practice_Er_M_S_Dandyan/Python/Pycharm/xml/main.py", line 69, in <module>
     print("l1 * l2 : ", l1*l2)
 TypeError: can't multiply sequence by non-int of type 'list'

• List allows Slice operator.

 #program to use slice operator List

 l1 = [10, 20, 30, 40, 50, 60, 70, 80, 90]
 print("l1         : ", l1)
 print("l1[ : : ]  : ", l1[ : : ])
 print("l1[2:10:3] : ", l1[ 2:10:3])
 print("l1[-9: : ] : ", l1[ -9: : ])
 print("l1[ : :-1] : ", l1[ : : -1])


 #output

 l1         :  [10, 20, 30, 40, 50, 60, 70, 80, 90]
 l1[ : : ]  :  [10, 20, 30, 40, 50, 60, 70, 80, 90]
 l1[2:10:3] :  [30, 60, 90]
 l1[-9: : ] :  [10, 20, 30, 40, 50, 60, 70, 80, 90]
 l1[ : :-1] :  [90, 80, 70, 60, 50, 40, 30, 20, 10]

• Element values in List can repeat

 #program 

 l1 = [10, 20, 30, 40, 50, 40, 30, 20, 10]
 print("l1 : ", l1)

 #output

 l1 :  [10, 20, 30, 40, 50, 40, 30, 20, 10]

• List are mutable, means we can modify members value

 #program to modify any particular member List

 l1 = [10, 20, 30, 40, 50, 40, 30, 20, 10]
 print("l1 : ", l1)
 l1[4] = 90
 l1[8] = 50
 print("l1 : ", l1)

 #output

 l1 :  [10, 20, 30, 40, 50, 40, 30, 20, 10]
 l1 :  [10, 20, 30, 40, 90, 40, 30, 20, 50]

• As Lists are mutable, so Insertion or Deletion of any member can be possible via List Built In Functions