1. Single branch structure

If < conditions >:
     < statement block >

2. Two branch structure

If < conditions >:
    < statement block >
else:
	< statement block >
Compact form: two branch structure for simple expressions
 < expression1 > If < condition > else < expression2 >
guess=eval(input())
print("guess" {} ". format(" right "if guess==99 else" wrong ")

3. Condition combination

x and y			#The logical sum of two conditions x and y
x or y			#Logical or of two conditions x and y
not x			#Logical negation of condition x

4. Program exception handling

num = eval(input("Please enter an integer:"))
print(num**2)
//When input'abc'The following error message appears:
Traceback (most recent call last):
  File "E:/python/CalBMI.py", line 2, in <module>
    print(num**2)
TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'int'

//Basic use of exception handling:
try:
	<Statement block1>
except	<Exception type>:(Exception type can not be written)
	<Statement block2>
	
try:
	num = eval(input("Please enter an integer:"))
	print(num**2)
except TypeError:
	print("Input is not an integer")

//Advanced use of exception handling:
try:
	<Statement block1>
except:
	<Statement block2>
else:
	<Statement block3>
finally:
	<Statement block4>
#finally Corresponding statement block4Certain execution
#else Corresponding statement block3Execute when no exception occurs

1. Ergodic cycle

• Extract the elements one by one from the traversal structure and put them in the loop variable

for <Loop variable>  in <Ergodic structure>
	<Sentence>

1)Count cycle:
for i in range(1,6,2):
	print("Hello:",i)
Hello: 1
Hello: 3
Hello: 5

2)String traversal loop:
for c in s:
	<Statement block>
for c in "python":
	print(c,end=",")
p,y,t,h,o,n,

3)List traversal loop:
for item in ls:
	<Statement block>
for item in [123,"PY",456]:
	print(item,end=",")
123,PY,456,

4)File traversal loop:
for line in fi:		#fi is a file identifier, traversing each line to generate a loop
	<Statement block>
for line in fi:
	print(line)		#Read one line of file at a time
//good
//very good
//Very nice

2. Condition cycle
1)

a=3
while a>0:
	a+=1;
	print(a)
4
5
...		(here CTRL + C Exit execution)

2) cycle control reserved word

• break jumps out and ends the current cycle
• Continue to end the current cycle and continue to execute the subsequent cycles

3. Advanced usage of circulation

for <variable> in <Ergodic structure>:
	<Statement block1>
else:
	<Statement block2>
	
while <condition>:
	<Statement block1>
else:
	<Statement block2>

• When the loop is not exited by the break statement, the else statement block is executed
• else statement block as reward for "normal" completion cycle
• Here, the use of else is similar to that in exception handling

for c in "PYTHON":
	if c =="T":
		continue;
		print(c,end="")
else:
	print("Normal exit")
//Output is:PYTHONNormal exit