Python 初识（二）

迭代器

# 1、字符创创建迭代器对象
str1 = 'liangdianshui'
iter1 = iter ( str1 )

# 2、list对象创建迭代器
list1 = [1,2,3,4]
iter2 = iter ( list1 )

# 3、tuple(元祖) 对象创建迭代器
tuple1 = ( 1,2,3,4 )
iter3 = iter ( tuple1 )

# for 循环遍历迭代器对象
for x in iter1 :
    print ( x , end = ' ' )

print('\n------------------------')
 
# next() 函数遍历迭代器
while True :
    try :
        print ( next ( iter3 ) )
    except StopIteration :
        break

输出：

l i a n g d i a n s h u i 
------------------------
1
2
3
4

list 生成式

list1=list ( range (1,31) )
print(list1)
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30]

# 语法
[expr for iter_var in iterable] 
[expr for iter_var in iterable if cond_expr]

list1=[x * x for x in range(1, 11)]
print(list1)
# [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

list1= [x * x for x in range(1, 11) if x % 2 == 0]
print(list1)
# [4, 16, 36, 64, 100]