注：以下内容为学习笔记，多数是从书本、资料中得来，只为加深印象，及日后参考。然而本人表达能力较差，写的不好。因非翻译、非转载，只好选原创，但多数乃摘抄，实为惭愧。但若能帮助一二访客，幸甚！
2012-12-17 星期一
1.读取文件
'''
Created on Dec 17, 2012
读取文件
@author: liury_lab
'''
# 最方便的方法是一次性读取文件中的所有内容放到一个大字符串中：
all_the_text = open('d:/text.txt').read()
print(all_the_text)
all_the_data = open('d:/data.txt', 'rb').read()
print(all_the_data)
# 更规范的方法
file_object = open('d:/text.txt')
try:
all_the_text = file_object.read()
print(all_the_text)
finally:
file_object.close()
# 下面的方法每行后面有‘\n’
file_object = open('d:/text.txt')
try:
all_the_text = file_object.readlines()
print(all_the_text)
finally:
file_object.close()
# 三句都可将末尾的'\n'去掉
file_object = open('d:/text.txt')
try:
#all_the_text = file_object.read().splitlines()
#all_the_text = file_object.read().split('\n')
all_the_text = [L.rstrip('\n') for L in file_object]
print(all_the_text)
finally:
file_object.close()
# 逐行读
file_object = open('d:/text.txt')
try:
for line in file_object:
print(line, end = '')
finally:
file_object.close()
# 每次读取文件的一部分
def read_file_by_chunks(file_name, chunk_size = 100):
file_object = open(file_name, 'rb')
while True:
chunk = file_object.read(chunk_size)
if not chunk:
break
yield chunk
file_object.close()
for chunk in read_file_by_chunks('d:/data.txt', 4):
print(chunk)
输出：
hello python
hello world
b'ABCDEFG\r\nHELLO\r\nhello'
hello python
hello world
['hello python\n', 'hello world']
['hello python', 'hello world']
hello python
hello worldb'ABCD'
b'EFG\r'
b'\nHEL'
b'LO\r\n'
b'hell'
b'o'
2012-12-18 星期二
2.写入文件
'''
Created on Dec 18, 2012
写入文件
@author: liury_lab
'''
# 最简单的方法
all_the_text = 'hello python'
open('d:/text.txt', 'w').write(all_the_text)
all_the_data = b'abcd1234'
open('d:/data.txt', 'wb').write(all_the_data)
# 更好的办法
file_object = open('d:/text.txt', 'w')
file_object.write(all_the_text)
file_object.close()
# 分段写入
list_of_text_strings = ['hello', 'python', 'hello', 'world']
file_object = open('d:/text.txt', 'w')
for string in list_of_text_strings:
file_object.writelines(string)
list_of_text_strings = ['hello', 'python', 'hello', 'world']
file_object = open('d:/text.txt', 'w')
file_object.writelines(list_of_text_strings)
2012-12-19 星期三
3.搜索和替换文件中的文本
# 将文件中的某个字符串改变成另一个
# 下面代码实现从一个特定文件或标准输入读取文件，然后替换字符串，然后写入一个指定的文件
import os, sys
nargs = len(sys.argv)
if not 3 <= nargs <= 5:
print('usage: %s search_text repalce_text [infile [outfile]]' % \
os.path.basename(sys.argv[0]))
else:
search_text = sys.argv[1]
replace_text = sys.argv[2]
input_file = sys.stdin
output_file = sys.stdout
if nargs > 3:
input_file = open(sys.argv[3])
if nargs > 4:
output_file = open(sys.argv[4], 'w')
for s in input_file:
output_file.write(s.replace(search_text, replace_text))
output_file.close()
input_file.close()
在MyEclipse + pyDev 环境下设置运行参数：
运行结果：
进一步提高效率：
# 进一步精简，一次性完成，不用循环，避免产生两个字符串的拷贝，提高速度和内存效率
nargs = len(sys.argv)
if not 3 <= nargs <= 5:
print('usage: %s search_text repalce_text [infile [outfile]]' % \
os.path.basename(sys.argv[0]))
else:
search_text = sys.argv[1]
replace_text = sys.argv[2]
input_file = sys.stdin
output_file = sys.stdout
if nargs > 3:
input_file = open(sys.argv[3])
if nargs > 4:
output_file = open(sys.argv[4], 'w')
output_file.write(input_file.read().replace(search_text, replace_text))
output_file.close()
input_file.close()
2012-12-20 星期四
4.从文件中读取指定行
# Python的标准库linecache模块非常适合这个任务
import linecache
the_line = linecache.getline('d:/FreakOut.cpp', 222)
print (the_line)
# linecache读取并缓存文件中所有的文本，若文件很大，而只读一行，则效率低下。
# 可显示使用循环, 注意enumerate从0开始计数，而line_number从1开始
def getline(the_file_path, line_number):
if line_number < 1:
return ''
for cur_line_number, line in enumerate(open(the_file_path, 'rU')):
if cur_line_number == line_number-1:
return line
return ''
the_line = linecache.getline('d:/FreakOut.cpp', 222)
print (the_line)
输出：
int Draw_Rectangle(int x1, int y1, int x2, int y2, int color)
int Draw_Rectangle(int x1, int y1, int x2, int y2, int color)
2012-12-21 星期五
5.Python 3.x 读取UTF-8文件，及统计文件行数
'''
Created on Dec 21, 2012
Python 读取UTF-8文件
统计文件的行数目
@author: liury_lab
'''
# -*- coding: utf-8 -*-
import codecs
# 对较小的文件，最简单的方法是将文件读入一个行列表中，然后计算列表的长度即可
count = len(codecs.open('d:/FreakOut.cpp', 'rU', 'utf-8').readlines())
print(count)
# 对较大的文件，可循环计数
count = -1
for count, line in enumerate(codecs.open('d:/FreakOut.cpp', 'rU', 'utf-8')):
pass
count += 1
print(count)
# 对于像windows结束标记有'\n'的，还可以有如下办法：
count = 0
the_file = codecs.open('d:/FreakOut.cpp', 'rb', 'utf-8')
while (True):
buffer = the_file.read(8192*1024)
if not buffer:
break
count += buffer.count('\n')
count += 1
the_file.close()
print(count)
2012-12-22 星期六
6.处理文件中的每个词
'''
Created on Dec 21, 2012
处理文件中的每个词
@author: liury_lab
'''
import codecs
the_file = codecs.open('d:/text.txt', 'rU', 'UTF-8')
for line in the_file:
for word in line.split():
print(word, end = "|")
the_file.close()
# 若词的定义有变，可使用正则表达式
# 如词被定义为数字字母，连字符或单引号构成的序列
import re
the_file = codecs.open('d:/text.txt', 'rU', 'UTF-8')
print()
print('************************************************************************')
re_word = re.compile('[\w\'-]+')
for line in the_file:
for word in re_word.finditer(line):
print(word.group(0), end = "|")
the_file.close()
# 封装成迭代器
def words_of_file(file_path, line_to_words = str.split):
the_file = codecs.open('d:/text.txt', 'rU', 'UTF-8')
for line in the_file:
for word in line_to_words(line):
yield word
the_file.close()
print()
print('************************************************************************')
for word in words_of_file('d:/text.txt'):
print(word, end = '|')
def words_by_re(file_path, repattern = '[\w\'-]+'):
the_file = codecs.open('d:/text.txt', 'rU', 'UTF-8')
re_word = re.compile('[\w\'-]+')
def line_to_words(line):
for mo in re_word.finditer(line):
yield mo.group(0) # 原书为return，发现结果不对，改为yield
return words_of_file(file_path, line_to_words)
print()
print('************************************************************************')
for word in words_by_re('d:/text.txt'):
print(word, end = '|')
输出：
2012-12-23 星期日
7.随机输入\输出及更新随机存取文件
'''
Created on Dec 21, 2012
随机输入输出
@author: liury_lab
'''
# 给定一个包含很多固定长度记录的大二进制文件，随机读取一条记录（不逐条读取）
the_file = open('d:/recon_0.yuv', 'rb')
record_size = 16
record_number = 6
the_file.seek(record_size * record_number)
buffer = the_file.read(record_size)
for ch in buffer:
print(ch, end = ' ')
结果：
# 给定一个包含很多固定长度记录的大二进制文件，想读取其中一条记录并且修改该条记录某些子段的值，然后写回文件。
# 方法：读取记录，解包，执行更新，然后重新组合成记录，找到正确位置，写入
import struct
format_string = '16b' # 一条记录是16个字节整数
the_file = open('d:/recon_0.yuv', 'r+b')
record_size = struct.calcsize(format_string)
record_number = 400
the_file.seek(record_size * record_number)
buffer = the_file.read(record_size)
fields = list(struct.unpack(format_string, buffer))
print(fields)
# 进行计算，并修改相关的子段
for i in range(0, 16):
fields[i] += 1
print(fields)
buffer = struct.pack(format_string, *fields)
the_file.seek(record_size * record_number)
the_file.write(buffer)
the_file.close()
结果：