From Array to List

PERL arrays are called lists in Python.

Here is a PERL program demonstrating various aspects of arrays.

@A=(10, 20, 30, 40, 3);
print $A[2],”\n”;
$N=@A;
print “$N\n”;

@A=();
$N=@A;
print “$N\n”;
print $A[2],”\n”;

The equivalent code in Python looks like -

A=[10,20,30,40,3]
print A[2]
print len(A)

A=[]
print len(A)
print A[2]

Apart from the differences mentioned in chapter 2, here are the additional changes.

1. Length of list in Python is obtained by using the ‘len’ function.
2. PERL is more forgiving than Python if the command seeks out-of-range elements of arrays/lists.

Python Shortcuts on Lists

Here we discuss a number of useful shortcuts related to lists in Python.

1. The ‘+’ symbol concatenates two lists.

a=[1,3,2,0]
b=[2,3,1,7]
print a+b

2. You can use ‘:’ to get sublist.

a=[1,3,4,9,6,2,0]
b=a[3:7]
print b

3. The following command gives a sublist from 3 to 7, skip 2.

a=[1,3,4,9,6,2,0]
b=a[3:7:2]
print b

4. The following command reverses the list.

a=[1,3,4,9,6,2,0]
b=a[::-1]
print b

Keywords ‘in’ and ‘del’

Keyword ‘in’

The keyword ‘in’ can be used to iterate over the keys or values. It checks wherher a number is in the list or not.

a=[3,4,9,1]

print 3 in a
print 100 in a

Keyword - del

The keyword del is used to remove a list element at a known index.

x=['a','b','c','d']
del x[2]
print x

Try -

a=[1,3,4,9,6,2,0]
print a
del a[2]
print a