Python Learning

Python tricks and tips Section 1: Lists Lesson 4: Negative indexing lists Code snippet to copy: a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] a[-3:-1]

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)

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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)

Python list slicing Step by step explanation of a "reverse a list" trick from previous post Perhaps the most interesting operations you can do with lists are 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 and stopping before the 1st element from the end.

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 😊. ➖➖➖➖➖➖➖➖➖➖➖➖➖➖ 👉Join @python_bds for more👈 *This channel belongs to @bigdataspecialist group

Python list slicing Step by step explanation of a "reverse a list" trick from previous post Perhaps the most interesting operations you can do with lists are 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 and stopping before the 1st element from the end.

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

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

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 tricks and tips Section 1: Lists Lesson 1: Reverse a list Code snippet to copy: a=[10,9,8,7] print(a[::-1])

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