文件读取

按字节读取

➜  file cat read_test.txt 
第1行
第2行
第3行

➜  file cat read_byte.py  
with open("read_test.txt") as f:
    print "read the first 3 bytes"
    print 'data is: ' + f.read(3)
    print 'file pointer is: ' + str(f.tell())
    print

    print "read the next 3 bytes"
    print 'data is: ' + f.read(3)
    print 'file pointer is: ' + str(f.tell())
    print

    f.seek(3)

    print "seek file pointer and read 1 bytes"
    print 'data is: ' + f.read(4)
    print 'file pointer is: ' + str(f.tell())

➜  file python read_byte.py 
read the first 3 bytes
data is: 第
file pointer is: 3

read the next 3 bytes
data is: 1�
file pointer is: 6

seek file pointer and read 1 bytes
data is: 1行
file pointer is: 7

第二次读取的中文不完整，所以出现了乱码

按行读取

➜  file cat read_test.txt 
第1行
第2行
第3行

➜  file cat read_line.py 
with open("read_test.txt") as f:
    print "read the first line"
    print 'data is: ' + f.readline().replace("\n", "")
    print 'file pointer is: ' + str(f.tell())
    print

    print "read the rest lines"
    for line in f.readlines():
        print 'data is: ' + line.replace("\n", "")
        print 'file pointer is: ' + str(f.tell())

➜  file python read_line.py 
read the first line
data is: 第1行
file pointer is: 8

read the rest lines
data is: 第2行
file pointer is: 23
data is: 第3行
file pointer is: 23

读取不会自动去除结尾的换行符

文件遍历

➜  file cat read_test.txt 
第1行
第2行
第3行

➜  file cat each_line.py
with open("read_test.txt") as f:
    for line in f:
        print line
➜  file python each_line.py 
第1行

第2行

第3行

文件写入

按字节写入

➜  file cat write_test.txt
cat: write_test.txt: No such file or directory

➜  file cat write_byte.py 
# encoding: utf-8

with open("write_test.txt", "wa") as f:
    print "write the first 3 bytes"
    f.write('你')

    print "write the next 3 bytes"
    f.write(u'好'.encode("utf-8"))
    f.write("\n")

    print "write unicode error"
    f.write(u'好')

➜  file python write_byte.py 
write the first 3 bytes
write the next 3 bytes
write unicode error
Traceback (most recent call last):
  File "write_byte.py", line 12, in <module>
    f.write(u'好')
UnicodeEncodeError: 'ascii' codec can't encode character u'\u597d' in position 0: ordinal not in range(128)

➜  file cat write_test.txt  
你好

文件写入默认使用ASCII编码，所以报错了

按行写入

➜  file cat write_test.txt
cat: write_test.txt: No such file or directory

➜  file cat write_line.py
# encoding: utf-8

with open("write_test.txt", "wa") as f:
    print "write the first line"
    f.writelines("第1行" + "\n")

    print "write the rest lines"
    f.writelines(["第2行" + "\n", "第3行" + "\n"])

➜  file python write_line.py 
write the first line
write the rest lines
➜  file cat write_test.txt  
第1行
第2行
第3行

写入不会自动在结尾添加换行符

读写模式

open 函数的 mode 参数

缓冲模式

open 函数的 buffering 参数

n 是大于 1 的数字