Python文件读写

读取文件

最方便的是一次性读入文件内容并放置到一个大字符串中

all_the_text = open('thefile.txt').read()#文本文件中的所有文本
all_the_text = open('thefile.txt'，'rb').read()#二进制文件中的所有数据

为了安全，最好给打开的文件指定一个名字 例如

file_object = open('thefile.txt')
#使用try/finally 语句是为了保证文件对象即使在读取中发生错误也可以被关闭 注意不要把open放到try/finally中
try:
    all_the_file = file_object.read()
finally:
    file_object.close()

最简单最快 最具Python风格的是逐行读取 并将内容放到列表中：

list_of_all_the_lines = file_object.readlines()
#这样读出的每行末尾都带有'\n'

也可以使用以下替代方案

list_of_all_the_lines = file_object.read().splitlines()
list_of_all_the_lines = file_object.read().split('\n')
list_of_all_the_lines = [L.rstrip('\n') for L in file_object]

#最简单的逐行处理文本文件的方法是用
for line in file_object:
    line = line.rstrip('\n')#去除每行末尾的'\n'
    line = line.rstrip()#去除每行末尾的空白符
    process line

 如果选择一次读取文件的一小部分，而不是全部，可以这么写

file_object = open('thefile.txt'，'rb')
try:
    while True:
        chunk = file_object.read(100)
        if not chunk:
            break
        do_something_with(chunk)
finally:
    file_object.close()

复杂的循环最好封装成生成器 但我们只能将逻辑的一部分进行封装 因为生成器的关键字yield 不被允许出现在tyr/finally的子语句try子句中

我们可以这样做

def read_file_by_chunks(filename,chunksize=100):
    file_object = open(filename,'rb')
    while True:
        chunk = file_object.read(chunksize)
        if not chunk:
            break
        yield chunk
    file_object.colse()

然后我们就可以这样使用

for chunk in read_file_by_chunks('abinfile'):
    do_something_with(chunk)

写入文件

最简单的将长字符串写入文本的方式

open('thefile.txt','w').write(all_the_text)
open('abinfile','wb').write(all_the_data) #写入二进制到文本

不过最好还是给文件对象指定一个好名字，这样就可以在完成操作后调用close()关闭文件对象

file_object = open('thefile.txt','w')
file_object.write(all_the_text)
file_object.colse()

如果要写入字符串列表而不是长字符串

file_object.writelines(list_of_text_strings)
open('abinfile','wb').writelines(list_of_data_string)

文件打开的一些方式

Modes	Description
r	Opens a file for reading only. The file pointer is placed at the beginning of the file. This is the default mode.
rb	Opens a file for reading only in binary format. The file pointer is placed at the beginning of the file. This is the default mode.
r+	Opens a file for both reading and writing. The file pointer will be at the beginning of the file.
rb+	Opens a file for both reading and writing in binary format. The file pointer will be at the beginning of the file.
w	Opens a file for writing only. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.
wb	Opens a file for writing only in binary format. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.
w+	Opens a file for both writing and reading. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing.
wb+	Opens a file for both writing and reading in binary format. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing.
a	Opens a file for appending. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing.
ab	Opens a file for appending in binary format. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing.
a+	Opens a file for both appending and reading. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing.
ab+	Opens a file for both appending and reading in binary format. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing.

 file 内建方法

SN	Methods with Description
1	file.close() Close the file. A closed file cannot be read or written any more.
2	file.flush() Flush the internal buffer, like stdio's fflush. This may be a no-op on some file-like objects.
3	file.fileno() Return the integer file descriptor that is used by the underlying implementation to request I/O operations from the operating system.
4	file.isatty() Return True if the file is connected to a tty(-like) device, else False.
5	file.next() Returns the next line from the file each time it is being called.
6	file.read([size]) Read at most size bytes from the file (less if the read hits EOF before obtaining size bytes).
7	file.readline([size]) Read one entire line from the file. A trailing newline character is kept in the string.
8	file.readlines([sizehint]) Read until EOF using readline() and return a list containing the lines. If the optional sizehint argument is present, instead of reading up to EOF, whole lines totalling approximately sizehint bytes (possibly after rounding up to an internal buffer size) are read.
9	file.seek(offset[, whence]) Set the file's current position.
10	file.tell() Return the file's current position
11	file.truncate([size]) Truncate the file's size. If the optional size argument is present, the file is truncated to (at most) that size.
12	file.write(str) Write a string to the file. There is no return value.
13	file.writelines(sequence) Write a sequence of strings to the file. The sequence can be any iterable object producing strings, typically a list of strings.

 

 参考 http://www.tutorialspoint.com/python/python_files_io.htm