Python 列表生成式、生成器与模块导入机制详解

l=[]
for i in range(100):
  l.append('egg%s' %i)
print(l)
​
l=['egg%s' %i for i in range(100)]
l=['egg%s' %i for i in range(1000) if i > 10]
print(l)

names=['egon','alex_sb','wupeiqi','yuanhao','lxx']
res=map(lambda x:x.upper(),names)  # map函数 映射
names=list(res)         #['EGON', 'ALEX_SB', 'WUPEIQI', 'YUANHAO', 'LXX']
print(names)
names=['egon','alex_sb','wupeiqi','yuanhao','lxx']
names=[name.upper() for name in names]   #列表生成式
print(names)
names=['egon','alex_sb','wupeiqi','yuanhao','lxx'] #列表生成式
names=[len(name) for name in names if not name.endswith('sb')]
print(names)
nums=[]                 #一般循环方法
with open('a.txt','r',encoding='utf-8') as f:
  for line in f:
    nums.append(len(line))
print(max(nums))
with open('a.txt','r',encoding='utf-8') as f:#列表生成式
  nums=[len(line) for line in f]
  print(max(nums))  #28
with open('a.txt','r',encoding='utf-8') as f:
  nums=(len(line) for line in f) #生成器表达式
  print(next(nums))  #15
  print(next(nums))  #17
  print(next(nums))  #13
  print(max(nums))  #28
  print(max(nums))  #空列表
  max(len(line) for line in f)  #去掉括号

import spam
spam.read1()

import spam
强调：之后的导入会直接引用第一次导入的结果，不会重复执行文件
import spam
print(spam)
模块中功能的执行始终以模块自己的名称空间为准
read1=111111    #money=1000
spam.read1()    #def read1():
          #  print('spam模块.read1：',money)
#结果：spam模块.read1： 1000

import spam as sm
sm.read1()
engine=input('>>: ').strip()
if engine == 'mysql':
  import mysql as db
else engine == 'oracle':
  import oracle as db
db.parse()

from spam import money,read1,read2,change
read1()​
from spam import *   #从模块中导入所有方法
read1()        #spam中：__all__=['money','read1'] 表示*能导入的方法，不写则表示能导入所有​

from spam import read1
money=1111111111
read1()   #结果：spam模块.read1： 1000
from ... import ......名字，拿到的名字可以不加前缀直接使用，使用起来更加方便, 但问题是容易与当前执行文件中相同的名字冲突
from spam import money
money=1111111111111111
print(money)    #1111111111111111,而不是1000

from spam import money as m
print(m)

#print(__name__)
__name__的值:
1、在文件被直接执行的情况下，等于'__main__'
2、在文件被导入的情况下，等于模块名
​
if __name__ == '__main__':
   print('文件被当中脚本执行啦。、。')
  read1()
else:
   print('文件被导入啦')
   read2()

import sys
sys.path.append(r'D:\code\SH_fullstack_s1\day14\dir1')
​
import m1
m1.f1()