详解Python中for循环的定义迭代方法

for <var> in <iterable>: # <iterable>是对象的集合——例如，列表或元组。
    <statement(s)> # 循环体

a = ['曹操', '孫権', '劉備']
for i in a:
    print(i)

iter('曹操孫権')                             # String
<str_iterator object at 0x036E2750>

iter(['曹操', '孫権', '劉備'])                # List
<list_iterator object at 0x036E27D0>

iter(('曹操', '孫権', '劉備'))                # Tuple
<tuple_iterator object at 0x036E27F0>

iter({'曹操', '孫権', '劉備'})                # Set
<set_iterator object at 0x036DEA08>

iter({'曹操': 1, '孫権': 2, '劉備': 3})       # Dict
<dict_keyiterator object at 0x036DD990>

iter(1)                                   # Integer
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not iterable

iter(1.1)                                  # Float
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'float' object is not iterable

iter(len)                                  # Built-in function
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'builtin_function_or_method' object is not iterable

list_ = ['曹操', '孫権', '劉備']

itr = iter(list_ )
itr
<list_iterator object at 0x031EFD10>

next(itr)
'曹操'
next(itr)
'孫権'
next(itr)
'劉備'

list_ = ['曹操', '孫権', '劉備']
itr = iter(list_)
list(itr)
['曹操', '孫権', '劉備']

itr = iter(list_)
tuple(itr)
('曹操', '孫権', '劉備')

itr = iter(list_)
set(itr)
{'劉備', '曹操', '孫権'}

d = {'曹操': 1, '孫権': 2, '劉備': 3}

for k in d:
    print(k)

for k in d:
    print(d[k])

#输出：
#1
#2
#3

for v in d.values():
    print(v)

#输出：
#1
#2
#3

i, j = (1, 2)

print(i, j)
1 2

for i, j in [(1, 2), (3, 4), (5, 6)]:
    print(i, j)

d = {'曹操': 1, '孫権': 2, '劉備': 3}

d.items()
dict_items([('曹操', 1), ('孫権', 2), ('劉備', 3)])

d = {'曹操': 1, '孫権': 2, '劉備': 3}
for k, v in d.items():
    print('k =', k, ', v =', v)

x = range(5)
x
range(0, 5)
type(x)
<class 'range'>

for n in x:
    print(n)

list(x)
[0, 1, 2, 3, 4]

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

list(range(5, 20, 3))
[5, 8, 11, 14, 17]

# 默认为1
list(range(5, 10, 1))
[5, 6, 7, 8, 9]

list(range(5, 10))
[5, 6, 7, 8, 9]

# 数值范围必须是可以正向迭代
list(range(-5, 5))
[-5, -4, -3, -2, -1, 0, 1, 2, 3, 4]

list(range(5, -5))
[]

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

for i in ['曹操', '孫権', '劉備']:
    if '孫' in i:
        break
    print(i)

for i in ['曹操', '孫権', '劉備']:
    if '孫' in i:
        continue
    print(i)

for i in ['曹操', '孫権', '劉備']:
    print(i)
else:
    print('结束。')

for i in ['曹操', '孫権', '劉備']:
    if i == '孫権':
        break
    print(i)
else:
    print('结束。')