Output of Python program | Set 6 (Lists)

Prerequisite - Lists in Python Predict the output of the following Python programs. These question set will make you conversant with List Concepts in Python programming language.

• Program 1 

list1 = ['physics', 'chemistry', 1997, 2000]
list2 = [1, 2, 3, 4, 5, 6, 7 ]
 
print "list1[0]: ", list1[0]        #statement 1
print "list1[0]: ", list1[-2]       #statement 2
print "list1[-2]: ", list1[1:]      #statement 3
print "list2[1:5]: ", list2[1:5]    #statement 4

• Output:

list1[0]:  physics
list1[0]:  1997
list1[-2]:  ['chemistry', 1997, 2000]
list2[1:5]:  [2, 3, 4, 5]

• Explanation: To access values in lists, we use the square brackets for slicing along with the index or indices to obtain required value available at that index.For N items in a List MAX value of index will be N-1. Statement 1 : This will print item located at index 0 in Output. Statement 2 : This will print item located at index -2 i.e.second last element in Output. Statement 3 : This will print items located from index 1 to end of the list. Statement 4 : This will print items located from index 1 to 4 of the list.
• Program 2 

list1 = ['physics', 'chemistry', 1997, 2000]
print "list1[1][1]: ", list1[1][1] #statement 1
print "list1[1][-1]: ", list1[1][-1] #statement 2

• Output:

list1[1][1]:  h
list1[1][-1]:  y

• Explanation: In python we can slice a list but we can also slice a element within list if it is a string. The declaration list[x][y] will mean that 'x' is the index of element within a list and 'y' is the index of entity within that string.
• Program 3 

list1 = [1998, 2002, 1997, 2000]
list2 = [2014, 2016, 1996, 2009]
print "list1 + list 2 = : ", list1 + list2   #statement 1
print "list1 * 2 = : ", list1 * 2  #statement 2

• Output:

list1 + list 2 = :  [1998, 2002, 1997, 2000, 2014, 2016, 1996, 2009]
list1 * 2 = :  [1998, 2002, 1997, 2000, 1998, 2002, 1997, 2000]

• Explanation: When addition(+) operator uses list as its operands then the two lists will get concatenated. And when a list id multiplied with a constant k>=0 then the same list is appended k times in the original list.
• Program 4

list1 = range(100, 110) #statement 1
print "index of element 105 is : ", list1.index(105)  #statement 2

• Output:

index of element 105 is :  5

• Explanation: Statement 1 : will generate numbers from 100 to 110 and append all these numbers in the list. Statement 2 : will give the index value of 105 in the list list1.
• Program 5 

list1 = [1, 2, 3, 4, 5]
list2 = list1
list2[0] = 0;
print "list1= : ", list1 #statement 2

• Output:

list1= :  [0, 2, 3, 4, 5]

• Explanation: In this problem, we have provided a reference to the list1 with another name list2 but these two lists are same which have two references(list1 and list2). So any alteration with list2 will affect the original list.