Python f.seek() 和 f.tell() 读取文本文件的每一行
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f.seek() and f.tell() to read each line of text file
提问by John
I want to open a file and read each line using f.seek()and f.tell():
我想打开一个文件并使用f.seek()and读取每一行f.tell()：
test.txt:
测试.txt：
abc
def
ghi
jkl
My code is:
我的代码是：
f = open('test.txt', 'r')
last_pos = f.tell() # get to know the current position in the file
last_pos = last_pos + 1
f.seek(last_pos) # to change the current position in a file
text= f.readlines(last_pos)
print text
It reads the whole file.
它读取整个文件。
采纳答案by lenik
ok, you may use this:
好的，你可以使用这个：
f = open( ... )
f.seek(last_pos)
line = f.readline() # no 's' at the end of `readline()`
last_pos = f.tell()
f.close()
just remember, last_posis not a line number in your file, it's a byte offset from the beginning of the file -- there's no point in incrementing/decrementing it.
请记住，last_pos它不是文件中的行号，而是从文件开头的字节偏移量——增加/减少它没有意义。
回答by Sean Johnson
Is there any reason why you have to use f.tell and f.seek? The file object in Python is iterable - meaning that you can loop over a file's lines natively without having to worry about much else:
你有什么理由必须使用 f.tell 和 f.seek 吗？Python 中的文件对象是可迭代的——这意味着你可以在本地循环文件的行而不必担心其他很多事情：
with open('test.txt','r') as file:
for line in file:
#work with line
回答by lenik
A way for getting current position When you want to change a specific line of a file:
一种获取当前位置的方法当您想更改文件的特定行时：
cp = 0 # current position
with open("my_file") as infile:
while True:
ret = next(infile)
cp += ret.__len__()
if ret == string_value:
break
print(">> Current position: ", cp)
回答by lotif
Skipping lines using islice works perfectly for me and looks like is closer to what you're looking for (jumping to a specific line in the file):
使用 islice 跳过行对我来说非常有效，并且看起来更接近您要查找的内容（跳转到文件中的特定行）：
from itertools import islice
with open('test.txt','r') as f:
f = islice(f, last_pos, None)
for line in f:
#work with line
Where last_pos is the line you stopped reading the last time. It will start the iteration one line after last_pos.
其中 last_pos 是您上次停止阅读的行。它将在 last_pos 后一行开始迭代。
