第六章第3讲：条件与循环（2）

1.断言

num1 = 20
assert num1 < 10

结果：

    assert num1 < 10
AssertionError

2.while：默认条件为真

# while 默认条件为真
name = ""
while not name:
    name = input("Please enter your name:")
print("hello %s" % name)

结果：

Please enter your name:Ann
hello Ann

# while 默认条件为真
# while 判断条件
# 语句
# demo：计算1到100的和
n =100
sum = 0
counter = 1
while counter <=n:
    sum = sum + counter
    counter +=1
print("1到 %d 之和为：%d" % (n,sum))

结果：

1到 100 之和为：5050

　　注意：使用while的时候，小心陷入无限循环

# while无限循环
var = 1
while var ==1:
    num = int(input("Please enter a number:"))
    print("The num is :")
print("Goodbye!")

或

while True:
    num = int(input("Please enter a number:"))
    print("The num is :")
print("Goodbye!")

　　while与else

count = 0
while count < 5:
    print(count,"小于5")
    count +=1
else:
    print(count,"大于5")

结果：

0 小于5
1 小于5
2 小于5
3 小于5
4 小于5
5 大于5

3.for语句

　for语句的格式：

　for <variable> in <sequences>：

　else:

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language = ["vb","c","c++","java","python"]
for x in language:
    print(x)

结果：

vb
c
c++
java
python

4.range函数

　range(上限，下限，步长)：下限不包含

# range函数
for number in range(1,5):
    print(number)
print("===================")
# range函数的简写
for number in range(5):
    print(number)
print("===================")
# range函数的应用
for number in range(1,10,2):
    print(number)

结果：

1
2
3
4
===================
0
1
2
3
4
===================
1
3
5
7
9

5.并行迭代

# 并行迭代
names = ["Alice","Bela","Bob","Dan"]
ages = [11,12,13,14]
for i in range(len(names)):
    print(names[i],"is",ages[i],"years old.")

结果：

Alice is 11 years old.
Bela is 12 years old.
Bob is 13 years old.
Dan is 14 years old.

　　借助zip函数快速处理并行迭代

# zip函数处理并行迭代
names = ["Alice","Bela","Bob","Dan","Ann"]
ages = [11,12,13,14]
for name,ages in zip(names,ages):
    print(name,"is",ages,"years old.")

结果：

Alice is 11 years old.
Bela is 12 years old.
Bob is 13 years old.
Dan is 14 years old.

6.按索引迭代

# 按索引迭代
names = ["Alice","Bela","Bob","Dan","Ann"]
index = 0
for name in names:
    if "ob" in name:
        names[index] = "Tom"
    index +=1
print(names)

结果：

['Alice', 'Bela', 'Tom', 'Dan', 'Ann']

7.continue:结束本次循环，进入下一个迭代循环

　break：结束循环（终止循环）

# continue
for i in range(5):
    print("========")
    print("i=",i)
    if i == 3:
        continue
    print("hello everyone!")

结果：

========
i= 0
hello everyone!
========
i= 1
hello everyone!
========
i= 2
hello everyone!
========
i= 3
========
i= 4
hello everyone!

# break

for i in range(5):
    print("========")
    print("i=", i)
    if i == 3:
        break
    print("hello everyone!")

结果：

========
i= 0
hello everyone!
========
i= 1
hello everyone!
========
i= 2
hello everyone!
========
i= 3

8.break与continue案例

案例1：

# break
names = ["Alice","Bob","Bela","Dan","Ann"]
for name in names:
    if name == "Bela":
        print("Hello Bela")
        break
    print("The student name is ",name)
else:
    print("no student name is Bela")
print("Done")

结果：

The student name is  Alice
The student name is  Bob
Hello Bela
Done

案例2：

# break
for letter in "python":
    if letter == "n":
        break
    print("The letter is ",letter)

结果：

The letter is  p
The letter is  y
The letter is  t
The letter is  h
The letter is  o

案例3：

# break
var =10
while var >0:
    print("The value is ",var)
    var -=1
    if var ==5:
        break
print("Byebye!")

结果：

The value is  10
The value is  9
The value is  8
The value is  7
The value is  6
Byebye!

continue案例

# continue
for letter in "python":
    if letter == "o":
        continue
    print("The letter is ",letter)

结果：

The letter is  p
The letter is  y
The letter is  t
The letter is  h
The letter is  n

第六章第3讲：条件与循环（2）

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