Python复习笔记—文件
1. open打开文件open(filename, mode)
mode：只读（r)，只写（w)，追加（a)，读写（r+），二进制读（rb，wb，ab, r+b)，
2. 读文件
read()，读全部文件
read()，读size个字节
readline()读开始一行
readlines()读所有行到一个list
3. 写文件
write(string)，写入字符串，非字符串必须先转换为字符串
4. 随机读写
seek(offset, from)，
from：0文件开始；1当前位置，2文件末尾
5. 安全读写
用open语句，会自动关闭文件，甚至是在发生异常的情况下
with open(filename, mode) as f :
dosomething(f)
6. 序列化和反序列化
pickle.dump(obj, f)，序列化到文件；
obj = pickle.load(f)，反序列化；
7. 例子
>>> #write file
>>> f = open('D:/temp/python_test.txt', 'w')
>>> f.write('abcdefghijklmnopqrstuvwxyz\r\n')
>>> f.write('0123456789\r\n') #\r\n is line separator on Windows
>>> val = ('value is', 12)
>>> f.write(str(val)) # nonstring object should be convert string first
>>> f.close()
>>> #read file
>>> f = open('D:/temp/python_test.txt', 'r')
>>> f.read()
"abcdefghijklmnopqrstuvwxyz\r\n0123456789\r\n('value is', 12)"
>>> f.seek(0, 0)
>>> f.tell()
0L
>>> f.readline()
'abcdefghijklmnopqrstuvwxyz\r\n'
>>> f.readlines()
['0123456789\r\n', "('value is', 12)"]
>>> f.seek(0, 0) # move to begin of the file
>>> f.read(3)
'abc'
>>> f.seek(4, 1) # skip 4 bytes
>>> f.read(1)
'h'
>>> f.seek(-2, 2) # Go to the 3rd byte before the end
>>> f.read(1)
'2'
>>> f.seek(0, 0)
>>>
>>> # read line by line
>>> for line in f :
print line
abcdefghijklmnopqrstuvwxyz
0123456789
('value is', 12)
>>> f.close()
>>> # read with 'with'
>>> with open('D:/temp/python_test.txt', 'r') as f:
for line in f :
print line
abcdefghijklmnopqrstuvwxyz
0123456789
('value is', 12)
>>> # serialize/unserialize object
>>> with open('D:/temp/python_test.txt', 'w') as f :
pickle.dump(, f)
>>> with open('D:/temp/python_test.txt', 'r') as f :
x = pickle.load(f)
print x
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