顺序查找（线性查找）
# _*_coding:utf-8_*_
def linear_search(li, val):
for ind, v in enumerate(li):
if v == val:
return ind
else:
return None
li = list(range(1000))
print(linear_search(li, 389))
# _*_coding:utf-8_*_
def linear_search(li, val):
for ind, v in enumerate(li):
if v == val:
return ind
else:
return None
li = list(range(1000))
print(linear_search(li, 389))