表达式

普通的表达式

def func(x,y):
    if x > y:
        return x
    else:
        return y

res = func(1,2)
print(res)

三元表达式

语法格式：条件成立时返回的值 if 条件 else 条件不成立时要返回的值

x = 1
y = 2

res = x if x > y else y
print(res)
egon = 18
alex = 80

res = 'egon是儿子' if egon < alex else 'alex是爸爸'
print(res)

列表生成式

格式：[expression for item in iterable in condition]

原代码：

l = ['alex_dsb','lxx_dsb','wxx_dsb','xxq','egon_dsb']
new_l = []
for name in l:
    if name.endswith('dsb'):
        new_l.append(name)

改进后：

l = ['egon_is_sb','egon_is_dsb','egon_is_superdsb','xxq','egon_dsb']

new_l = [name for name in l]  # 最基础的列表生成式
new_l = [name for name in l if name.endswith('sb')]

print(new_l)

把所有小写字母变成大写

l = ['egon_is_sb','egon_is_dsb','egon_is_superdsb','xxq','egon_dsb']
new_l = [name.upper() for name in l ]
print(new_l)

去掉所有名字的_sb后缀

l = ['egon_is_sb','egon_is_sb','egon_is_superd_sb','xxq','egon_sb']

new_l = [name.replace('_sb','') for name in l]
print(new_l)

字典生成式

keys = ['name','age','gender']

dic = {key:None for key in keys}
print(dic)
items = [('name','egon'),('age',18),('gender','male')]

dict = {k:v for k,v in items if k!='gender'}
print(dict)

集合生成式

keys = ['name','age','gender']
set1 = {key for key in keys}
print(set1,type(set1))

元组生成式（没有元组生成式）

g = (i for i in range(10) if i > 3)
print(g,type(g))

# 输出：<generator object <genexpr> at 0x01D63450> <class 'generator'>

生成器表达式

g = (i for i in range(10) if i > 3)
# ！！！！！！！强调！！！！！！！
# 此时g的内部，一个值都没有
# 只有next的时候，才会产生一个值

print(g)
print(next(g))
print(next(g))
print(next(g))
print(next(g))
方式一：
with open(r'内容.txt',mode='rt',encoding='UTF-8') as f:
    res = 0
    for line in f:
        res += len(line)
    print(res)

方式二：
with open(r'内容.txt',mode='rt',encoding='UTF-8') as f:

    res = sum([len(line) for line in f])
    print(res)

方式三：效率高
with open(r'内容.txt', mode='rt', encoding='UTF-8') as f:
    # g = (len(line) for line in f)
    # print(g)
    # res = sum(g)
    # print(res)
    # res = sum((len(line) for line in f))
    # 上述可以简写为如下格式
    res = sum(len(line) for line in f)
    print(res)

思维导图（点击链接）