Prerequisite – Lists in Python
Predict the output of the following Python programs.
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Program 1
Python
list = [1, 2, 3, None, (1, 2, 3, 4, 5), ['Geeks', 'for', 'Geeks']]
print len(list)
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Output:
6
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Explanation:
The beauty of python list datatype is that within a list, a programmer can nest another list, a dictionary or a tuple. Since in the code there are 6 items present in the list the length of the list is 6.
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Program 2
Python
list = ['python', 'learning', '@', 'Geeks', 'for', 'Geeks']
print list[::]
print list[0:6:2]
print list[ :6: ]
print list[ :6:2]
print list[ ::3]
print list[ ::-2]
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Output:
['python', 'learning', '@', 'Geeks', 'for', 'Geeks'] ['python', '@', 'for'] ['python', 'learning', '@', 'Geeks', 'for', 'Geeks'] ['python', '@', 'for'] ['python', 'Geeks'] ['Geeks', 'Geeks', 'learning']
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Explanation:
In python list slicing can also be done by using the syntax listName[x:y:z] where x means the initial index, y-1 defines the final index value and z specifies the step size. If anyone of the values among x, y and z is missing the interpreter takes default value.
Note:
1. For x default value is 0 i.e. start of the list.
2. For y default value is length of the list.
3. For z default value is 1 i.e. every element of the list.
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Program 3
Python
d1 = [10, 20, 30, 40, 50]
d2 = [1, 2, 3, 4, 5]
print d1 - d1
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Output:
No Output
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Explanation:
Unlike addition or relational operators not all the arithmetic operators can use lists as their operands. Since – minus operator can’t take lists as its operand no output will be produced. Program will produce following error.
TypeError: unsupported operand type(s) for -: 'list' and 'list'
- Program 4
Python
list = ['a', 'b', 'c', 'd', 'e']
print list[10:]
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Output:
[]
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Explanation:
As one would expect, attempting to access a member of a list using an index that exceeds the number of members (e.g., attempting to access list[10] in the list above) results in an IndexError. However, attempting to access a slice of a list at a starting index that exceeds the number of members in the list will not result in an IndexError and will simply return an empty list.
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Program 5
Python
list = ['a', 'b', 'c']*-3
print list
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Output:
[]
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Explanation:
A expression list[listelements]*N where N is a integer appends N copies of list elements in the original list. If N is a negative integer or 0 output will be a empty list else if N is positive list elements will be added N times to the original list.
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