Python 标准库 fileinput与文件迭代器_python

import fileinput

for line in fileinput.input(filename):
    process(line)

import fileinput

for line in fileinput.input("D:/Users/data.txt"):
    print(line)

#打开文件，一次写入多行内容
f = open("D:/Users/data.txt",'w')
content = ['append information1\n','append information2']
f.writelines(content)
f.close()

#打开文件，通过文件迭代器遍历文件
f = open("D:/Users/data.txt",'r')
for line in f:
    print('content:',line)
# 或者 将读取内容转化为字符串列表 效果类似 readlines
lines = list(f)
print(lines)
#关闭文件
f.close()

content: append information1
content: append information2

In [35]: d = {'a':1,'b':2}

In [36]: r = d.setdefault('c',3) # r: 3

In [37]: r
Out[37]: 3

In [38]: d
Out[38]: {'a': 1, 'b': 2, 'c': 3}


In [39]: r = d.setdefault('c',33) # r:3，已经存在'c':3的键值对，所以setdefault时d无改变

In [40]: r
Out[40]: 3

In [41]: d
Out[41]: {'a': 1, 'b': 2, 'c': 3}