python基础学习-三元表达式+生成式

一、三元表达式

1、普通和三元表达式区别：

1.普通的表达式

def func(x,y):
    if x > y:
        return x
    else:
        return y
​
res = func(1,2)
print(res)

2、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' if egon < alex else 'alex'
print(res)

二、生成式

1、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)
​
#操作案例：
#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)

2、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)

3、集合生成式

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

4、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'>

5、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)