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控制语句

Warning

！！不要用浮点数比较相等！！

判断

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if condition:
    print()
elif condition:
    print()
else:
    print()

Example

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age = 20

if age > = 6:
    print('teenager')
elif age >= 18:
    print('adult')
else:
    print('kid')

还可以简写

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if x:
    print('True')

或

if x: print('True')

只要 x 是非零数值、非空字符串、非空list、非空tuple，也不是None，就判断为True，否则为False

循环

for

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for x in Iterable:
   do sth

Example

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Li = [1, 2, 3, 4, 5, 6]
sum = 0
for x in Li:
    sum += x
print(sum)

# 21

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sum = 0
for x in [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]:
    sum = sum + x
print(sum)

#55

range()

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>>> range(5)
0, 1, 2, 3, 4
>>> list(range(5))
[0, 1, 2, 3, 4]

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# 从1加到100

sum = 0
for x in range(101):
    sum = sum + x
print(sum)

# 5050

while

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while condition:
    do sth

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sum = 0
n = 99

while n > 0:
    sum = sum + n
    n = n - 2
print(sum)

break

跳出整个循环，且不执行else子句

continue

跳出本次循环

else

else 子句会在循环不满足条件退出时执行

但如果 break 跳出循环时，不会执行else子句

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sum = 0
n = 99

while n > 0:
    sum = sum + n
    n = n - 2


else:
    print('else')    # 循环结束后会执行这句话
print(sum)

--------------------------------

# Output:
else
2500

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sum = 0
n = 99

while n > 0:
    sum = sum + n
    n = n - 2
    if n < 10:
        break   # n 小于 10的时候会跳出循环，并且不会执行 else 子句
else:
    print('else')
print(sum)

---------------------------------

# Output:
2475

pass

pass 语句什么也不做。当语法上需要一个语句，但程序需要什么动作也不做时，可以使用它。

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>>> while True:
...     pass  # Busy-wait for keyboard interrupt (Ctrl+C)

>>> class MyEmptyClass:
...     pass

>>> def initlog(*args):
...     pass   # Remember to implement this!