Ebook: Python Tricks 😎

Python and ML MCQ with Answer

Python Programming college notes🔥

Python for Everybody (PY4E)
by Charles R. Severance (aka Dr. Chuck)


🎬 17 sections with multiple video lessons
👨‍🏫 Prof. Dr. Charles R. Severance
✅ Completely free

https://www.py4e.com/lessons

Python tricks and tips
Section 1: Lists
Lesson 1: Reverse a list

Code snippet to copy:
a=[10,9,8,7]
print(a[::-1])

Previous image shows valuable info but it's from 2019. I am not saying that situation has changed significantly but here is a little better overview what happened in previous few years.

Python list slicing
Step by step explanation of a "reverse a list" trick from previous post

Perhaps the most interesting operation you can do with lists is called slicing.
IT gives you opportunity to get portion of your list.
For example:

🔹 Step 1: Getting list slice
x = ['a','b','c','d','e']
print(x[0]) #first element - a
print(x[0:1]) #first element, but we have explicitly set both start and end - ['a']
print(x[0:2]) #first two elements - ['a', 'b']

🔹 Step 2: Starting from the end
WE can also go through list from end to beginning, in this case, we use negative indexes:

print(x[-3:-1]) # This will return the slice starting from the 3rd element from the end (c) and stopping before the 1st element from the end (e).

Output: ['c', 'd']

🔹 Step 3: Introducing increment
We can also ad increment to slicing. In all previous examples increment was one, but what if we want to get every second element of the list?

print(x[0:5:2]) # starting from first element, ending with last one, with increment of 2

Output: ['a', 'c', 'e']

🔹 Step 4: Omitting slicing parameters
As you can see, full slicing formula would be:

my_list[start_index:end_index:increment]

But we can omit (leave out/exclude) any of those 3 parameters
For example:

print(x[:3]) # We omitted first parameter,  this will print first 3 elements of the list 
print(x[3:]) # this will print rest 2 elements  (from 4th to end)
print(x[:3:2]) # this will print first 3 elements with increment 2
print(x[:]) # no start and end index, this will print entire list!
print(x[::-1]) # this will also print entire list, but with negative increment, starting from last to first one -> REVERSED LIST

Output:
['a', 'b', 'c']
['d', 'e']
['a', 'c']
['a', 'b', 'c', 'd', 'e']
['e', 'd', 'c', 'b', 'a']

I put some effort into creating this so please let me know if you learned something valuable and if you like this type of content 😊.

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Python tricks and tips
Section 1: Lists
Lesson 2: Flatten a list

Code snippet to copy:
import itertools
a = [[1, 2], [3, 4], [5, 6]]
b = list(itertools.chain.from_iterable(a))
print(b)

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Join @python_bds for more

Python tricks and tips
Section 1: Lists
Lesson 3: Combining different lists

Code snippet to copy:
a=[‘a’,’b’,’c’,’d’]
b=[‘e’,’f’,’g’,’h’]
for x, y in zip(a, b):
print(x,y)