Python Learning Key Note

1.variable

a = 2

It doesn't need decear variable type, and don't need ";" in the end boolean type will be True and Flase, first world is upper case.

2.operation

a / b result will always be a float type

3.fstring

a = 2
b = 3.5
s = f"result is {a} and {b}"

f-string, put f in front of string can combine different type of variable into one string, in python, you can not use "+" to append different type after string, such "result" + a will generate error.

4.conditions

if x > 10:
  print("x bigger than 10")
elif x == 10:
  print("x is equal to 10")
else:
  print("x is smaller than 0")

if condition and else will folow with a ":"

5. logical operator

and or not, if x > 10 and x < 20, if not x == 10

6. list

color = ["red", "blue", "green"]
color[0] //red
color[-1] //green
color.append("yellow"); //[red, blue, green, yellow]
color.extend(["black", "white"]) //[red, blue, green, yellow, black, white]

7.loop

for c in color:
  print(c)

for number in range(1, 3)
 print(number)        //1, 2
for number in range(1,5, 2)
 print(number)  //1, 3, 5

while number < 10:
  print(number)
  number += 1

8.function

def myFunction():  //def for creating function and : in end of function name
"""Document string myfunction""" //this three " will put into doucment for this function
  print("Hello")
  print("Here")
def setColor(color):
  print(f"your color is {color}")
you can call function with setColor("red") or setColor(color = "red")
def getColor:
 return color

9.scope and indentation

for above function, print hello and print here is in the same scope similar like

def myFunction() {
    print("Hello")
    print("Here")
}

if move print("Here") allign with def like

def myFunction():
  print("Hello")
print("Here")

print is out side the myFunction scope and is not belong to part of the function. In python, indentation apply to everything scope including if else or for loop.

num = 2
def add():
 num = 3
add()
print(number) //2

in python if you use the same variable name inside a function, it will be another different local variable, so this print result will still be 2

if you want to access the global variable and change it

def add():
 global num //declare a global num that tell the function num is exist somewhere outside the function
 num = 3

local variable only happens inside fun, if it's in a condition statement, the variable is also see outside scope

num = 2
if num > 1:
  another_num = 2
print(another_num)   // here you will see another num is 2 because inside if scope the value is available outside.

10.modules

in file color.py

mycolor = ["red","green", "blue"]

in file main.py

import color
print(color.mycolor)
// or from color import mycolor
print(mycolor)

11.dictionary

students = {
  "id1": "student1"
  "id2": "student2"
}
print(students["id1"]) //student1
students["id3"] = "student3" //add id3 and student3 to dictionary
students["id2"] = ""  //edit dictionary id2 to empty
empty_dictionary = {}
for key in students //for loop will only access the key here
 print(key) //"id1" "id2"
 print(students[key]) // "student1" "student2"

12.tuple

color = ("red", green, "blue")
print(color[1]) //print green

13.class

class Student:
 def __init__(self, id):  //constuctor
    self.id = id
 def input_name(self, name): //method
    self.name = name

student = Student(1)