mirror of
https://github.com/namibia/awesome-cheatsheets.git
synced 2024-12-31 13:11:54 +00:00
Added python cheat sheet to the languages folder.
I intentionally skipped the OOPS concept as it consists more data which is making cheat book but not sheet, Please do mention if I'm missing, I will add them.
This commit is contained in:
Jay
GitHub
parent
be167bc112
commit
d590c82ecb
321
languages/python.md
Normal file
321
languages/python.md
Normal file
@ -0,0 +1,321 @@
|
||||
# Python
|
||||
|
||||
* Python is an interpreted, high-level and general-purpose, dynamically typed programming language
|
||||
|
||||
* It is also Object oriented, modular oriented and a scripting language.
|
||||
|
||||
* In Python, everything is considered as an Object.
|
||||
|
||||
* A python file has an extension of .py
|
||||
|
||||
* Python follows Indentation to separate code blocks instead of flower brackets({}).
|
||||
|
||||
* We can run a python file by the following command in cmd(Windows) or shell(mac/linux).
|
||||
|
||||
`python <filename.py>`
|
||||
|
||||
#### By default, the python doesn't require any imports to run a python file.
|
||||
|
||||
## Create and execute a program
|
||||
|
||||
1. Open up a terminal/cmd
|
||||
1. Create the program: nano/cat > nameProgram.py
|
||||
1. Write the program and save it
|
||||
1. python nameProgram.py
|
||||
|
||||
<br>
|
||||
|
||||
### Basic Datatypes
|
||||
|
||||
| Data Type | Description |
|
||||
| --------- | ----------- |
|
||||
| int | Integer values [0, 1, -2, 3] |
|
||||
| float | Floating point values [0.1, 4.532, -5.092] |
|
||||
| char | Characters [a, b, @, !, `] |
|
||||
| str | Strings [abc, AbC, A@B, sd!, `asa] |
|
||||
| bool | Boolean Values [True, False] |
|
||||
| char | Characters [a, b, @, !, `] |
|
||||
| complex | Complex numbers [2+3j, 4-1j] |
|
||||
|
||||
<br>
|
||||
|
||||
## Keywords
|
||||
<br>
|
||||
|
||||
| Keyword | Description |
|
||||
| --------- | ----------- |
|
||||
| break | used to exit loop and used to exit|
|
||||
| char | basic declaration of a type character |
|
||||
| const | prefix declaration meaning variable can not be changed|
|
||||
| continue | go to bottom of loop in for, while loops|
|
||||
| class | to define a class|
|
||||
| def | to define a function|
|
||||
| elif | shortcut for (else if) used in else if ladder |
|
||||
| else | executable statement, part of "if" structure |
|
||||
| float | basic declaration of floating point|
|
||||
| for | executable statement, for loop|
|
||||
| from | executable statement, used to import only specific objects from a package|
|
||||
| if | executable statement|
|
||||
| import | to import modules|
|
||||
|pass| keyword to specify noting is happening in the codeblock, generally used in classes|
|
||||
|return | executable statement with or without a value|
|
||||
|while| executable statement, while loop|
|
||||
<br>
|
||||
|
||||
## Operators
|
||||
|
||||
<br>
|
||||
|
||||
| Operator | Description |
|
||||
|-|-|
|
||||
| ( ) | grouping parenthesis, function call, tuple declaration |
|
||||
| [ ] | array indexing, also declaring lists etc.|
|
||||
| ! | relational not, complement, ! a yields true or false |
|
||||
| ~ | bitwise not, ones complement, ~a |
|
||||
| \- | unary minus, - a |
|
||||
| \+ | unary plus, + a |
|
||||
| \* | multiply, a * b |
|
||||
| / | divide, a / b |
|
||||
| % | modulo, a % b |
|
||||
| \+ | add, a + b |
|
||||
| \- | subtract, a - b |
|
||||
| << | shift left, left operand is shifted left by right operand bits |
|
||||
| \>> | shift right, left operand is shifted right by right operand bits|
|
||||
| < | less than, result is true or false, a %lt; b
|
||||
| <= | less than or equal, result is true or false, a <= b
|
||||
| \> | greater than, result is true or false, a > b
|
||||
| \>= | greater than or equal, result is true or false, a >= b
|
||||
| == | equal, result is true or false, a == b
|
||||
| != | not equal, result is true or false, a != b
|
||||
| & | bitwise and, a & b
|
||||
| ^ | bitwise exclusive or XOR, a ^ b
|
||||
| \| | bitwise or, a | b
|
||||
| &&, and | relational and, result is true or false, a < b && c >= d
|
||||
| \|\|, or | relational or, result is true or false, a < b \|\| c >= d |
|
||||
| = | store or assignment |
|
||||
| += | add and store |
|
||||
| -= | subtract and store |
|
||||
| *= | multiply and store |
|
||||
| /= | divide and store|
|
||||
| %= | modulo and store|
|
||||
| <<= | shift left and store|
|
||||
| \>>= | shift right and store|
|
||||
| &= | bitwise and and store|
|
||||
| ^= | bitwise exclusive or and store|
|
||||
| \|= | bitwise or and store|
|
||||
| , | separator as in ( y=x,z=++x )|
|
||||
|
||||
### Basic Data Structures
|
||||
|
||||
### List
|
||||
|
||||
- List is a collection which is ordered and changeable. Allows duplicate members.
|
||||
|
||||
|
||||
- Lists are created using square brackets:
|
||||
|
||||
```py
|
||||
thislist = ["apple", "banana", "cherry"]
|
||||
```
|
||||
|
||||
- List items are ordered, changeable, and allow duplicate values.
|
||||
|
||||
- List items are indexed, the first item has index `[0]`, the second item has index `[1]` etc.
|
||||
|
||||
- The list is changeable, meaning that we can change, add, and remove items in a list after it has been created.
|
||||
|
||||
- To determine how many items a list has, use the `len()` function.
|
||||
|
||||
- A list can contain different data types:
|
||||
```py
|
||||
list1 = ["abc", 34, True, 40, "male"]
|
||||
```
|
||||
- It is also possible to use the list() constructor when creating a new list
|
||||
```py
|
||||
thislist = list(("apple", "banana", "cherry")) # note the double round-brackets
|
||||
```
|
||||
### Tuple
|
||||
- Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
|
||||
- A tuple is a collection which is ordered and unchangeable.
|
||||
- Tuples are written with round brackets.
|
||||
```py
|
||||
thistuple = ("apple", "banana", "cherry")
|
||||
```
|
||||
- Tuple items are ordered, unchangeable, and allow duplicate values.
|
||||
- Tuple items are indexed, the first item has index `[0]`, the second item has index `[1]` etc.
|
||||
- When we say that tuples are ordered, it means that the items have a defined order, and that order will not change.
|
||||
|
||||
- Tuples are unchangeable, meaning that we cannot change, add or remove items after the tuple has been created.
|
||||
- Since tuple are indexed, tuples can have items with the same value:
|
||||
- Tuples allow duplicate values:
|
||||
```py
|
||||
thistuple = ("apple", "banana", "cherry", "apple", "cherry")
|
||||
```
|
||||
- To determine how many items a tuple has, use the `len()`function:
|
||||
```py
|
||||
thistuple = ("apple", "banana", "cherry")
|
||||
print(len(thistuple))
|
||||
```
|
||||
- To create a tuple with only one item, you have to add a comma after the item, otherwise Python will not recognize it as a tuple.
|
||||
```py
|
||||
thistuple = ("apple",)
|
||||
print(type(thistuple))
|
||||
|
||||
#NOT a tuple
|
||||
thistuple = ("apple")
|
||||
print(type(thistuple))
|
||||
```
|
||||
- It is also possible to use the tuple() constructor to make a tuple.
|
||||
```py
|
||||
|
||||
thistuple = tuple(("apple", "banana", "cherry")) # note the double round-brackets
|
||||
print(thistuple)
|
||||
```
|
||||
|
||||
### Set
|
||||
- Set is a collection which is unordered and unindexed. No duplicate members.
|
||||
- A set is a collection which is both unordered and unindexed.
|
||||
```py
|
||||
thisset = {"apple", "banana", "cherry"}
|
||||
```
|
||||
- Set items are unordered, unchangeable, and do not allow duplicate values.
|
||||
- Unordered means that the items in a set do not have a defined order.
|
||||
|
||||
- Set items can appear in a different order every time you use them, and cannot be referred to by index or key.
|
||||
|
||||
- Sets are unchangeable, meaning that we cannot change the items after the set has been created.
|
||||
- Duplicate values will be ignored.
|
||||
- To determine how many items a set has, use the `len()` method.
|
||||
```py
|
||||
thisset = {"apple", "banana", "cherry"}
|
||||
|
||||
print(len(thisset))
|
||||
```
|
||||
- Set items can be of any data type:
|
||||
```py
|
||||
set1 = {"apple", "banana", "cherry"}
|
||||
set2 = {1, 5, 7, 9, 3}
|
||||
set3 = {True, False, False}
|
||||
set4 = {"abc", 34, True, 40, "male"}
|
||||
```
|
||||
- It is also possible to use the `set()` constructor to make a set.
|
||||
```py
|
||||
thisset = set(("apple", "banana", "cherry")) # note the double round-brackets
|
||||
```
|
||||
### Dictionary
|
||||
- Dictionary is a collection which is unordered and changeable. No duplicate members.
|
||||
- Dictionaries are used to store data values in key:value pairs.
|
||||
- Dictionaries are written with curly brackets, and have keys and values:
|
||||
```py
|
||||
thisdict = {
|
||||
"brand": "Ford",
|
||||
"model": "Mustang",
|
||||
"year": 1964
|
||||
}
|
||||
```
|
||||
- Dictionary items are presented in key:value pairs, and can be referred to by using the key name.
|
||||
```py
|
||||
thisdict = {
|
||||
"brand": "Ford",
|
||||
"model": "Mustang",
|
||||
"year": 1964
|
||||
}
|
||||
print(thisdict["brand"])
|
||||
```
|
||||
- Dictionaries are changeable, meaning that we can change, add or remove items after the dictionary has been created.
|
||||
- Dictionaries cannot have two items with the same key.
|
||||
- Duplicate values will overwrite existing values.
|
||||
- To determine how many items a dictionary has, use the `len()` function.
|
||||
```py
|
||||
print(len(thisdict))
|
||||
```
|
||||
- The values in dictionary items can be of any data type
|
||||
```py
|
||||
thisdict = {
|
||||
"brand": "Ford",
|
||||
"electric": False,
|
||||
"year": 1964,
|
||||
"colors": ["red", "white", "blue"]
|
||||
}
|
||||
```
|
||||
|
||||
### Conditional branching
|
||||
|
||||
```py
|
||||
if condition:
|
||||
pass
|
||||
elif condition2:
|
||||
pass
|
||||
else:
|
||||
pass
|
||||
```
|
||||
### Loops
|
||||
|
||||
Python has two primitive loop commands:
|
||||
1. while loops
|
||||
2. for loops
|
||||
|
||||
#### While loop
|
||||
- With the `while` loop we can execute a set of statements as long as a condition is true.
|
||||
- Example: Print i as long as i is less than 6
|
||||
```py
|
||||
i = 1
|
||||
while i < 6:
|
||||
print(i)
|
||||
i += 1
|
||||
```
|
||||
- The while loop requires relevant variables to be ready, in this example we need to define an indexing variable, i, which we set to 1.
|
||||
- With the `break` statement we can stop the loop even if the while condition is true
|
||||
- With the continue statement we can stop the current iteration, and continue with the next.
|
||||
|
||||
- With the else statement we can run a block of code once when the condition no longer is true.
|
||||
|
||||
#### For loop
|
||||
- A for loop is used for iterating over a sequence (that is either a list, a tuple, a dictionary, a set, or a string).
|
||||
|
||||
- This is less like the for keyword in other programming languages, and works more like an iterator method as found in other object-orientated programming languages.
|
||||
|
||||
- With the for loop we can execute a set of statements, once for each item in a list, tuple, set etc.
|
||||
```py
|
||||
fruits = ["apple", "banana", "cherry"]
|
||||
for x in fruits:
|
||||
print(x)
|
||||
```
|
||||
- The for loop does not require an indexing variable to set beforehand.
|
||||
- To loop through a set of code a specified number of times, we can use the range() function.
|
||||
- The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends at a specified number.
|
||||
- The range() function defaults to increment the sequence by 1, however it is possible to specify the increment value by adding a third parameter: range(2, 30, 3).
|
||||
- The else keyword in a for loop specifies a block of code to be executed when the loop is finished.
|
||||
A nested loop is a loop inside a loop.
|
||||
|
||||
- The "inner loop" will be executed one time for each iteration of the "outer loop":
|
||||
|
||||
```py
|
||||
adj = ["red", "big", "tasty"]
|
||||
fruits = ["apple", "banana", "cherry"]
|
||||
|
||||
for x in adj:
|
||||
for y in fruits:
|
||||
print(x, y)
|
||||
```
|
||||
- for loops cannot be empty, but if you for some reason have a for loop with no content, put in the pass statement to avoid getting an error.
|
||||
|
||||
```py
|
||||
for x in [0, 1, 2]:
|
||||
pass
|
||||
```
|
||||
|
||||
### Function definition
|
||||
```py
|
||||
def function_name():
|
||||
return
|
||||
```
|
||||
### Function call
|
||||
|
||||
```py
|
||||
function_name()
|
||||
```
|
||||
|
||||
* We need not to specify the return type of the function.
|
||||
* Functions by default return `None`
|
||||
* We can return any datatype.
|
||||
Loading…
Reference in New Issue
Block a user