List

List

Mutable, list can be modified

List needs to be in square bracket [], for example: [1,2,3,4,5] or [‘a’,’b’,’c’] or [1,2,3,’a’,’b’,’10’]

List is a sequence, iterable

l=[‘a’,’b’,’c’]

l[0]=“a”

l[1]=“b”

l[2]=“c”

It is zero based indexing, index starts from zero

List can be iterated through:

for i in l:
    print(i)

Convert to List, use function list()

For example:

n=12345

list(n) becomes [1,2,3,4,5]

List is an object, meaning it has methods and attributes that can be invoked

To see all methods, type

help(<list variable>)

In Jupyter notebook, to see list of methods or attributes

Press shift key after enter <list variable>.

>>> squares = [1, 4, 9, 16, 25]
>>> squares
[1, 4, 9, 16, 25]
>>> squares[0] # indexing returns the item
1
>>> squares[-1]
25
>>> squares[-3:] # slicing returns a new list
[9, 16, 25]
>>> squares[:]
[1, 4, 9, 16, 25]
>>> squares + [36, 49, 64, 81, 100]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
cubes = [1, 8, 27, 65, 125] # something's wrong here
>>> 4**3 # the cube of 4 is 64, not 65!
64
>>> cubes[3] = 64 # replace the wrong value
>>> cubes 
[1, 8, 27, 64, 125]
>>> cubes.append(216) # add the cube of 6
>>> cubes.append(7**3) # and the cube of 7
>>> cubes
[1, 8, 27, 64, 125, 216, 343]
>>> letters = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
>>> letters
['a', 'b', 'c', 'd', 'e', 'f', 'g']
>>> # replace some values
>>> letters[2:5] = ['C', 'D', 'E']
>>> letters
['a', 'b', 'C', 'D', 'E', 'f', 'g']
>>> # now remove them
>>> letters[2:5] = []
>>> letters
['a', 'b', 'f', 'g']
>>> # clear the list by replacing all the elements with an empty list
>>> letters[:] = []
>>> letters
[]
>>> letters = ['a', 'b', 'c', 'd']
>>> len(letters)
4
>>> a = ['a', 'b', 'c']
>>> n = [1, 2, 3]
>>> x = [a, n]
>>> x
[['a', 'b', 'c'], [1, 2, 3]]
>>> x[0]
['a', 'b', 'c']
>>> x[0][1]
‘b’

Fibonacci series:

the sum of two elements defines the next

a, b = 0, 1
fib=[]
while True:
#    print(a)
    if len(fib)>=10:
        break
    else:
        fib.append(a)
    a, b = b, a+b 
    print(fib[-1], end=" ")
    

running it will display:

0 1 1 2 3 5 8 13 21 34