Added a List Comprehension topic

basics/README.md

@@ -27,6 +27,7 @@ to learn more about whatever you want after studying it.
 19. [Exceptions](exceptions.md)
 20. [Classes](classes.md)
 21. [Docstrings](docstrings.md)
+22. [List Comprehension](list-comprehension.md)
 
 ***
 

basics/list-comprehension.md

@@ -0,0 +1,77 @@
+# List Comprehension
+
+
+## Definition
+List comprehensions creates a new list from an existing list that is a shorter syntax than normal. It also processes the list much faster than using a for loop.
+
+
+## Without List Comprehension
+```python
+animals = ["dog", "cat", "giraffe", "donkey", "ape"]
+arr = []
+
+for i in animals:
+  if len(i) == 3:
+    arr.append(i)
+
+print(arr)
+```
+```python
+['dog', 'cat', 'ape']
+```
+The example above shows a list of animals and the for loop iterates through the list of animals and the if statement filters the list and only adds the animal if their name is exactly 3 characters long.
+
+## With List Comprehension
+```python
+animals = ["dog", "cat", "giraffe", "donkey", "ape"]
+
+arr = [i for i in animals if len(i) == 3]
+print(arr)
+```
+```python
+['dog', 'cat', 'ape']
+```
+The example above does exactly the same thing but is in a much more concise syntax where it iterates through the list of animals and appends to the new list if their name is exactly 3 characters long.
+
+## Syntax
+
+newlist = [**expression** for **item** in **iterable** if **condition**]
+This is the usual form in which list comprehension is used.
+
+**Expression:** It is the current item for each iteration but also serves as the outcome which can be manipulated before it becomes added to the new list.
+```python
+animals = ["DOG", "CAT", "GIRAFFE", "DONKEY", "APE"]
+
+arr = [i.lower() for i in animals if len(i) == 3]
+print(arr)
+```
+```python
+['dog', 'cat', 'ape']
+```
+The **i** is essentially the **item** which is an animal in each iteration where it checks if the animal's name is 3 characters long and if it does it **also** changes that animal name to all lower case before it finally appends or adds it to the list.
+
+**Iterable:** The iterable is the object that is being iterated over and can be any iterable object such as a set, list, tuple etc.
+```python
+arr = [i for i in range(5)]
+print(arr)
+```
+```python
+[0, 1, 2, 3, 4]
+```
+This essentially adds 0 to 4 to the new array with range(5).
+
+**Condition** The condition is a sort of filter that is specified to get the specific data that is wanted.
+```python
+arr = [i for i in range(10) if i < 5]
+print(arr)
+```
+```python
+[0, 1, 2, 3, 4]
+```
+For this example the condition is that only the numbers that is less than 5 would get put into the array.
+
+## Summary
+- List comprehensions are a good way to shorten code
+- They are versatile when it comes to iterating through iterable datasets
+- Not only can you filter out data with a condition you can also change the data before it gets added to the new list
+- List comprehensions normally follow: newlist = [**expression** for **item** in **iterable** if **condition**]