Python: How to convert a dictionary into a list of key-value

Using the list() function, we can convert a dictionary into a list of key-value tuple.

>>> x = {'a':1, 'b':2}
>>> x
{'a': 1, 'b': 2}
>>> y = list(x.items())
>>> y
[('a', 1), ('b', 2)

To convert back into dictionary, use the dict() function.

>>> z = dict(y)
>>> z
{'a': 1, 'b': 2}

How to choose a random item from a sequence in Python

To choose a random item from a list, use random.choice().

Here is an example.

>>> items = ['Proton', 'Honda', 'Toyota', 'Nissan']
>>> random.choice(items)
'Nissan'
>>> random.choice(items)
'Proton'
>>> random.choice(items)
'Toyota'

Another example of usage is to choose a random file from a directory.

>>> random.choice(os.listdir("C:"))
'ubuntu'
>>> random.choice(os.listdir("C:"))
'tex4ht'

The intersection of two Python lists using Set

Set is unordered unique collection of objects.

We can use Set to find the intersection of two lists/tuples.

Suppose that we have two lists.

>>> x = [1, 2, 3, 4, 5]
>>> y = [2, 6, 7, 3]

To find the intersection of the two lists, first change both x and y to the Set type, then use the intersection method (&).

>>> set(x) & set(y)
{2, 3}

If we need the output in list type, apply the list command, to the output.

>>> list(set(x) & set(y))
[2, 3]

How to sort a Python tuple

Python tuple is immutable. Therefore, it cannot be changed.

To sort a Python tuple, we can create a new list using sorted() method.

If we still need it as a tuple, just apply tuple() to the new list.

>>> z = (1, 4, 3, 7, 2, 12, -3, 3)
>>> sorted_z = tuple(sorted(z))
>>> sorted_z
(-3, 1, 2, 3, 3, 4, 7, 12)

Convert Strings to Integers/Floats in Python

Strings to integer

To convert a string to an integer:

>>> x = '1234'
>>> int(x)
1234

Strings to float

To convert a string to float:

>>> x = '1234'
>>> float(x)
1234.0

>>> y = '1234.678'
>>> float(y)
1234.6780000000001

but, convertion of '1234.678' to integer using int() will gives an error.

>>> int(y)
Traceback (most recent call last):
File "<pyshell#4>", line 1, in <module>
int(y)
ValueError: invalid literal for int() with base 10: '1234.678'

A workaround is by first converting to float, then to integer:

>>> y = '1234.678'
>>> int(float(y))
1234

List/tuple of strings to list of integers

1. Using list comprehension
   >>> x = ['07', '11', '13', '14', '28']
   >>> [int(i) for i in x]
   [7, 11, 13, 14, 28]
2. Using map
   >>> x = ['07', '11', '13', '14', '28']
   >>> list(map(int, x))
   [7, 11, 13, 14, 28]
   Mix of integers and floats
   >>> x = ['7.424124', '11', '13.423', '14.53453656', '28.2']
   >>> list(map(int, map(float, x)))
   [7, 11, 13, 14, 28]

List/tuple of strings to list of floats

1. Using list comprehension
   >>> x = ['7.424124', '1', '13.423', '14.53453656', '28.2']
   >>> [float(i) for i in x]
   [7.4241239999999999, 1.0, 13.423,
   14.534536559999999, 28.199999999999999]
   
2. Using map
   >>> x = ['7.424124', '1', '13.423', '14.53453656', '28.2']
   >>> list(map(float, x))
   [7.4241239999999999, 1.0, 13.423,
   14.534536559999999, 28.199999999999999]

Unzip a Python list

Suppose that you have a list with tuples as the member.

>>> test = [('x',1), ('y',2), ('z',3)]

We can unzip the list by using zip() in conjunction with the * operator.

>>> a, b = zip(*test)
>>> a
('x', 'y', 'z')
>>> b
(1, 2, 3)

Python: Initialize list and tuple values

This tutorial will show on how to give a Python list an initial value.

To initialize a ten items list with values set to 0:

myList = [0]*10

If we need to have 5 items of a list with the value 0 and the rest 5 with the value 1:

myList = [0]*5 + [1]*5

To initialize a ten items tuple with values set to 0:

myTuple = (0,)*10

If we need to have 5 item in a tuple with the value 0 and the rest 5 with the value 1:

myTuple = (0,)*5 + (1,)*5

For list, don't forget the comma ','. It means one item.