Python中readall python中readall函数

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mob64ca13feda16 2024-02-28 16:38:01

文章标签 Python中readall python中有readall吗 python Python 读取文件 文章分类 Python 后端开发

关于，python中，文件被open打开后

再去调用read()，需要注意的是：

只需要调用一次read()，即可（读取出）获得文件的，所有的，内容了。

示例代码如下：#!/usr/bin/python

# -*- coding: utf-8 -*-

"""

Function:

【整理】关于python中文件open后去调用read()时需要知道的事情：只需调用一次即可获得文件的全部内容

https://www.crifan.com/python_file_open_then_read_once_will_read_all_file_content

Author: Crifan Li
Version: 2013-09-23
Contact: https://www.crifan.com/contact_me/
"""
import os
import fnmatch
#import re
def findTailContainSomeStr():
#for fName in os.listdir('E:/Dev_Root/python/answer_question/from_mail/qiu-yang.zhao/')
#for fName in os.listdir('./')
#for fName in os.listdir("E:\\Dev_Root\\python\\answer_question\\from_mail\\qiu-yang.zhao\\")
#for fName in os.listdir("E:\\Dev_Root\\python\\answer_question\\from_mail\\qiu-yang.zhao")
for fName in os.listdir("E:\\Dev_Root\\python\\answer_question\\from_mail\\qiu_yang_zhao\\"):
print "fName=",fName;
if fnmatch.fnmatch(fName, '*.pdf'):
#open(name[, mode[, buffering]])
#fhandle = open (fName)
fhandle = open (fName, 'rb')
print "fhandle=",fhandle
readOutFirst = fhandle.read();
#print "readOutFirst=",readOutFirst; # this line will print ALL file content, here is toooooo much, will make cmd crash, so comment it out
print "len(readOutFirst)=",len(readOutFirst)
readOutSecond = fhandle.read();
print "readOutSecond=",readOutSecond; # readOutSecond=
#above, readOutSecond is empty, for:
#fileHandler.read() will read ALL file content, once
#so, after one read(), not content left, so next read(), only return empty(null)
#so, use empty string to find something, will return -1
#so use follow:
print readOutFirst.find('xxx') #470644
allFileContent = readOutFirst
#print readOutSecond.find('trailer')
print allFileContent.find('yyy') #470525
# here, give your Python mannual explanation:
# file.read([size])
# Read at most size bytes from the file (less if the read hits EOF before obtaining size bytes).
# If the size argument is negative or omitted, read all data until EOF is reached.
# The bytes are returned as a string object.
# An empty string is returned when EOF is encountered immediately.
# (For certain files, like ttys, it makes sense to continue reading after an EOF is hit.)
# Note that this method may call the underlying C function fread() more than once in an effort
# to acquire as close to size bytes as possible.
# Also note that when in non-blocking mode,
#less data than was requested may be returned, even if no size parameter was given.
# Note
# This function is simply a wrapper for the underlying fread() C function,
# and will behave the same in corner cases, such as whether the EOF value is cached.
fhandle.close()
#whole output is:
#
# fName= xxx.pdf
# fhandle= 
# len(readOutFirst)= 475293
# readOutSecond=
# 470644
# 470525
# fName= findTailContainSomeStr.py
if __name__ == "__main__":
findTailContainSomeStr();

【总结】

这种事情的发生，其实：

和你自己是否知道此python的read()这个api的详细功能，关系不是很大

而和你是否掌握学习方法，关系很大。

换句话说，如果你学习python，是参考了，类似我的这样的帖子

中的：

后，掌握了，基本的学习方法后，

你在使用read()这个函数之前，就会去查查Python的自带的Mannual，然后可以查到，

（我已经贴在代码中出来的）

file.read([size])Read at most size bytes from the file (less if the read hits EOF before obtaining size bytes). If the size argument is negative or omitted, read all data until EOF is reached. The bytes are returned as a string object. An empty string is returned when EOF is encountered immediately. (For certain files, like ttys, it makes sense to continue reading after an EOF is hit.) Note that this method may call the underlying C function fread() more than once in an effort to acquire as close to size bytes as possible. Also note that when in non-blocking mode, less data than was requested may be returned, even if no size parameter was given.
Note
This function is simply a wrapper for the underlying fread() C function, and will behave the same in corner cases, such as whether the EOF value is cached.

的内容了，就可以看到这句：If the size argument is negative or omitted, read all data until EOF is reached

知道是：

调用read()时，如果不指定size参数，则会一直读，知道文件末尾（EOF）

即，直接读取文件的全部内容了。

即，read()不是读单个字节，而是文件的所有的内容。

所以，此处，既然调用了一次read()了

已经获得了文件的全部的内容了。

那么如果再次调用，必然是一个字节也读取不到：

因为已经（文件指针都指）到文件末尾了，没有更多的内容（字节）供你读了。

所以，必然返回空或-1等值了。

所以，总的说就是：

正常的写代码，学习的思路是：