control flow —— The second day of self-study

• 1. control flow
• • 1.1 The operator
  • 1.2 Boolean operator
  • 1.3 if sentence
  • 1.3 Loop statement
  • 1.4 The import module
• 2. function
• • 2.1 Function format
  • 2.2 Local and global scope
  • 2.2 exception handling

1. control flow

1.1 The operator

“ Comparison operator ” Compare two values , Evaluate to a Boolean value .

The operator meaning == be equal to != It's not equal to < Less than > Greater than <= Less than or equal to >= Less than or equal to

1.2 Boolean operator

The operator meaning and And or or not Not

1.3 if sentence

if Statement by if、elif、else form .

if "a" == "b":
print("a == b")
elif 2 != 2:
print("2!=2")
elif 2 < 1:
print("2 < 1")
elif 2 > 3:
print("2 > 3")
elif 2 <= 1:
print("2 <= 1")
elif 2 >= 3:
print("2 >= 3")
elif True and False:
print("True and False")
elif False or False:
print("False or False")
elif not True:
print("not True")
else:
print("nothing is right")

1.3 Loop statement

while True:
print("Your are right")
for i in range(10):
if i == 2:
continue
if i == 5:
break;
print(i)

1.4 The import module

• import random Import random modular

import random
i = random.randint(1, 10)
print(i)

• from random import * Import random All methods in the module

from random import *
i = randint(1, 10)
print(i)

2. function

2.1 Function format

def Method name ( Parameters )：
Method body
return Return value

2.2 Local and global scope

 Arguments and variables assigned in the called function , At the end of the function “ Local scope ”.
Variables assigned outside all functions , Belong to “ Global scope ”. Variables in local scope , go by the name of “ local variable ”.
Variables in global scope , go by the name of “ Global variables ”.
If you need to modify global variables within a function , Just use global sentence .
Yes 4 Rules , To distinguish whether a variable is in local scope or global scope ：
1． If the variable is used in the global scope （ That is, outside of all functions ）, It is always a global variable .
2． If in a function , There are... For this variable global sentence , It's a global variable .
3． otherwise , If the variable is used for an assignment statement in a function , It's a local variable .
4． however , If the variable is not used in the assignment statement , It's a global variable .

2.2 exception handling

try：
Code block
except Error code ：
Code block
finally:
Code block