分支判断、循环

if

>>> x = int(input("Please enter an integer: "))

Please enter an integer: 42

>>> if x < 0:

...      x = 0

...      print('Negative changed to zero')

... elif x == 0:

...      print('Zero')

... elif x == 1:

...      print('Single')

... else:

...      print('More')

...

More

for，python里for只用来遍历集合，不能做索引循环

>>> # Measure some strings:

... words = ['cat', 'window', 'defenestrate']

>>> for w in words:

...     print(w, len(w))

...

cat 3

window 6

defenestrate 12

range(),python里的数字for循环，python里for只用来遍历集合，不能做索引循环

>>> for i in range(5):

...     print(i)

...

0

1

2

3

4

range(起始,结束,间隔)

range(5, 10)

   5 through 9



range(0, 10, 3)

   0, 3, 6, 9



range(-10, -100, -30)

  -10, -40, -70

pathon里的索引遍历集合

>>> a = ['Mary', 'had', 'a', 'little', 'lamb']

>>> for i in range(len(a)):

...     print(i, a[i])

...

0 Mary

1 had

2 a

3 little

4 lamb

 break、continue

>>> for n in range(2, 10):

...     for x in range(2, n):

...         if n % x == 0:

...             print(n, 'equals', x, '*', n//x)

...             break

...     else:

...         # loop fell through without finding a factor

...         print(n, 'is a prime number')

...

2 is a prime number

3 is a prime number

4 equals 2 * 2

5 is a prime number

6 equals 2 * 3

7 is a prime number

8 equals 2 * 4

9 equals 3 * 3



>>> for num in range(2, 10):

...     if num % 2 == 0:

...         print("Found an even number", num)

...         continue

...     print("Found a number", num)

Found an even number 2

Found a number 3

Found an even number 4

Found a number 5

Found an even number 6

Found a number 7

Found an even number 8

Found a number 9

pass为空语句，用来站位，添在语法必须有语句有不想写语句的地方

>>> while True:

...     pass  # Busy-wait for keyboard interrupt (Ctrl+C)

...

>>> class MyEmptyClass:

...     pass

...

>>> def initlog(*args):

...     pass   # Remember to implement this!

...