Explanation of Python condition and loop statement
- 2021-12-04 10:47:43
- OfStack
1. Python conditional statement
An Python conditional statement is a block of code that determines execution by the execution results of one or more statements. In Python programming, if statement is used to control the execution of program. Python does not support the switch statement, so when there are multiple conditional decisions, you can only use elif for programming. The basic form of the if statement is:
if ( Conditional expression ):
Conditional statement
elif ( Additional conditions ):
Conditional statement
else:
Conditional statement
Example:
a = 1
if type(a) == int: # Judge a Is it plastic
print(' It's plastic surgery ') # If a Is shaping, executing the conditional statement
elif type == float: # Judge a Whether it is floating point type
print(' Is a floating-point type ') # If a Is a floating-point type, execute the conditional statement
else: # Any type except shaped floating point type
print(' Ha ha ') # Execute the conditional statement
# Output result: for shaping
1.1 pass Statement
The if statement cannot be empty, and you don't want to execute anything in the statement block after the colon. You can use the pass statement to avoid errors. Example:
a = 0
if a == 0:
pass
else:
print('hello')
print('end')
# Output result : end
2. Python for Loop Statement
The for loop is used to traverse any sequence of items, such as strings or lists. The for loop judges one condition at a time. Example of dictionary loop traversal:
person = {"name":"mj","age":31,"hobby":"dance"}
# Get all of the dictionary key value Value
for i,v in person.items():
print(i)
print(v)
# Output:
name
mj
age
31
hobby
dance
2.1 for nested loop
A nested loop is a loop within a loop, and the inner loop is executed once every time the outer loop iterates. Example:
# Use for Cyclic printing 99 Multiplication table
for i in range(1,10):
for j in range(1,i+1):
print("{}*{}={}".format(j,i,i*j),end=' ')
print()
"""
# Output:
1*1=1
1*2=2 2*2=4
1*3=3 2*3=6 3*3=9
1*4=4 2*4=8 3*4=12 4*4=16
1*5=5 2*5=10 3*5=15 4*5=20 5*5=25
1*6=6 2*6=12 3*6=18 4*6=24 5*6=30 6*6=36
1*7=7 2*7=14 3*7=21 4*7=28 5*7=35 6*7=42 7*7=49
1*8=8 2*8=16 3*8=24 4*8=32 5*8=40 6*8=48 7*8=56 8*8=64
1*9=9 2*9=18 3*9=27 4*9=36 5*9=45 6*9=54 7*9=63 8*9=72 9*9=81
"""
3. Python while Loop Statement
The while loop execution statement can be a single statement or a block of statements. As long as the condition is true, we can execute 1 group of statements. If the conditional statement is always true, the loop will execute indefinitely, for example:
while (1):
print(' Miss ')
Output:
Miss
Miss
Miss
...
"""
3.1 while Loop Nesting
Print a 99 multiplication table instance using the while statement:
i =1
while (i<=9):
j=1
while (j<=i):
print("{}*{}={}".format(j,i,i*j),end=' ')
j+=1
print()
i+=1
"""
# Output:
1*1=1
1*2=2 2*2=4
1*3=3 2*3=6 3*3=9
1*4=4 2*4=8 3*4=12 4*4=16
1*5=5 2*5=10 3*5=15 4*5=20 5*5=25
1*6=6 2*6=12 3*6=18 4*6=24 5*6=30 6*6=36
1*7=7 2*7=14 3*7=21 4*7=28 5*7=35 6*7=42 7*7=49
1*8=8 2*8=16 3*8=24 4*8=32 5*8=40 6*8=48 7*8=56 8*8=64
1*9=9 2*9=18 3*9=27 4*9=36 5*9=45 6*9=54 7*9=63 8*9=72 9*9=81
"""
4. break statement
The break statement is used in the for and while loop statements to terminate the loop. Example:
# for Loop statement :
list = ['for','while','else','break','continue']
for x in list:
if x == 'while':
break
print(x)
# Output: for
# while Loop statement:
i = 0
while (i<10):
print('happy')
i += 1
if i == 2:
break
# Output:
happy
happy
5. continue statement
The continue statement jumps out of this loop, and break jumps out of the entire loop. That is, continue is the remaining statement that skips the current loop and proceeds to the next loop. Example:
# Do not print continue
list = ['for','while','else','break','continue']
for b in list:
if b == 'while':
continue
print(b)
# Output:
for
else
break
continue
You can use the continue statement to skip some loops, such as I want to print odd numbers between 0 and 10:
n = 0
while (n<10):
n += 1
if n%2==0:
continue
print(n)
# Output:
1
3
5
7
9
Summarize
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