Python学习（七）：生成器表达式（expr for iner_var in iterable if cond_expr）

列表解析：[expr for iter_var in iterable if cond_expr]

生成器表达式：(expr for iter_var in iterable if cond_expr) 

J = 'aadsjnk'
S = 'asadasbxjscj'

def number(self,J,S):
    setJ = set(J)
    return sum(s in setJ for s in S)

print(number(0,J,S))


>>>9

• 交叉配对样例

rows = [1,2,3,7]
def cols():
    yield 56
    yield 2
    yield 1

x_product_pairs = ((i,j) for i in rows for j in cols())
for pair in x_product_pairs:
    print(pair)

输出：

• 重构样例

寻找文件最长的行,(核心代码）

f = open('/etc/python_code','r')
longest = max(len(x.strip()) for x in f)
f.close()
return longest

Reference:

yield：https://www.jianshu.com/p/d09778f4e055

set(): http://www.runoob.com/python/python-func-set.html

sum(): http://www.runoob.com/python/python-func-sum.html