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Mosh的Python课程笔记(3)--Control Flow

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Comparison Operators

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>>> 10 > 3
True
>>> 10 >= 3
True
>>> 10 < 20
True
>>> 10 == 10
True
>>> 10 == "10" 
False
>>> 10 != "10" 
True
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>>> "bag" > "apple" 
True
>>> "bag" == "BAG"  
False
>>> ord("b") 
98  
>>> ord("B") 
66

Chaining Comparison Operators

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# age should be between 18 and 65
age = 22
if 18 <= age < 65:
    print("Eligible")

Conditional Statements

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temperature = 15
if temperature > 30:
    print("It is warm")
    print("Drink water")

elif temperature > 20:
    print("It's nice")

else:
    print("It's cold")
    
print("Done")

Ternary Operator

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age = 2

# if age >= 18:
#     message = "Eligible"
# else:
#     message = "Not eligible"

message = "Eligible" if age >= 18 else "Not eligible"

print(message)

Logical Operators

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# logical operators: and, or, not

high_income = True
good_credit = False
student = False

if (high_income or good_credit) and not student:
    print("Eligible")
else:
    print("Not eligible")

Short-circuit Evaluation

多条件判断时：

and 前面的 expression 为 False, 则不再(执行)判断后面的expression

or 前面的 expression 为 True, 则不再(执行)判断后面的expression

For Loops

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for number in range(1, 10, 2):		# step: 2
    print("Attempt", number, number * ".")

输出：

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Attempt 1 .
Attempt 3 ...
Attempt 5 .....
Attempt 7 .......
Attempt 9 .........

For…Else

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successful = False
for number in range(3):
    print("Attempt")
    if successful:
        print("Successful")
        break
else:
    print("Attempted 3 times and failed.")

如果一直没有执行break，就执行下面的else

输出结果：

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Attempt
Attempt
Attempt
Attempted 3 times and failed

Nested Loops

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for x in range(5):
    for y in range(3):
        print(f"({x}, {y})")

输出结果

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(0, 0)
(0, 1)
(0, 2)
(1, 0)
(1, 1)
(1, 2)
(2, 0)
(2, 1)
(2, 2)
(3, 0)
(3, 1)
(3, 2)
(4, 0)
(4, 1)
(4, 2)

Iterables

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# Iterable : range(), string, list...
for x in "Python":
    print(x)

for x in [1, 2, 3, 4]:
    print(x)

输出：

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P
y
t
h
o
n
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4

While Loops

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command = ""
while command.lower() != "quit":
    command = input(">")
    print("ECHO", command)

输出结果：

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>2+2
ECHO 2+2
>3*4    
ECHO 3*4
>quit   
ECHO quit

Infinite Loops

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while True:
    command = input(">")
    print("ECHO", command)
    if command.lower() == "quit":
        break

Exercise

编写一段code，输出1~10之间（不含10）的偶数，如下：

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We have 4 even numbers