python常用内建函数

# 普通人的做法
list = [1, 2, 3, 4, 5, 6]
index = 0
for i in list:
    print(‘下标%s‘ % index, i)
    index += 1

# 大佬的做法
list = [1, 2, 3, 4, 5, 6]
for i, j in enumerate(list):
    print(‘下标%s‘ % i, j)

# 普通人的做法
list1 = [1, 2, 3, 4, 5, 6]
list2 = [2, 3, 4, 5, 6, 7]
list3 = [3, 4, 5, 6, 7, 8]
for i in list1:
    for j in list2:
        for k in list3:
            if i + j + k == 10:
                print(i, j, k)

# 大佬的做法
from itertools import product
for i, j, k in product(list1, list2, list3):
    if i + j + k == 10:
        print(i, j, k)

#普通人的做法
na = 2
while True:
    print(na)
    na +=1

#大佬的做法
from itertools import count
for i in count(2):#参数:表示从几开始
    print(i)

#普通人都做法
res = ‘ABC‘
while True:
    for i in res:
        print(i)

#大佬的做法
from itertools import cycle
for i in cycle(‘ABC‘):
    print(i)

#普通人都做法
list = [1,2,3,4,5,6]
for i in list:
    if i==list[2]:
        for j in range(10):
            print(‘1‘,list[2])

#大佬的做法
from itertools import repeat
list = [1,2,3,4,5,6]
res = repeat(list[2],10)#参数一:表示从几开始,参数二:表示重复次数
for i in res:
    print(‘2‘,i)

1234
---
aadd
---
sadsad
---
asdasdad

# 普通人的做法
def test():
    with open(‘a.txt‘, ‘r‘) as fp:
        for i, line in enumerate(fp):
            # 跳过无意义的 ‘---‘ 分隔符
            if i % 2 == 0:
                yield line.strip()
for i in test():
    print(i)

# 大佬的做法
from itertools import islice
# islice(seq, start, end, step) 函数和数组切片操作*（ list[start:stop:step] ）有着几乎一模一样的参数。
# 如果需要在循环内部进行隔行处理的话，只要设置第三个递进步长参数 step 值为 2 即可（默认为 1 ）*。
def parse_titles_v2():
    with open(‘a.txt‘, ‘r‘) as fp:
        # 设置 step=2，跳过无意义的 ‘---‘ 分隔符
        for line in islice(fp, 0, None, 2):
            yield line.strip()
for i in parse_titles_v2():
    print(i)

# 普通人的做法
list = [1, 2, 3, 4, 5, 6]
for i in list:
    if i == 4:
        break
    else:
        print(i)

# 大佬的做法
from itertools import takewhile
list = [1, 2, 3, 4, 5, 6]
for i in takewhile(lambda x: x != 4, list):#参数一:限制条件函数,list表
    print(i)

#普通人的做法
v1 = [11,22,33]
v2 = [44,55,66]
all = v1+v2
for c in all:
    print(c)

#大佬的做法
from itertools import chain
v1 = [11,22,33]
v2 = [44,55,66]
new_list = chain(v1,v2)
for c in new_list:
    print(c)