Question

Is seems that the mmap interface only supports readline(). If I try to iterate over the object I get character instead of complete lines.

什么是“慢慢慢”方法可以按线读出一粒的立案线?

import sys
import mmap
import os


if (len(sys.argv) > 1):
  STAT_FILE=sys.argv[1]
  print STAT_FILE
else:
  print "Need to know <statistics file name path>"
  sys.exit(1)


with open(STAT_FILE, "r") as f:
  map = mmap.mmap(f.fileno(), 0, prot=mmap.PROT_READ)
  for line in map:
    print line # RETURNS single characters instead of whole line

Answer 1

简化<条码>mmap 是

with open(STAT_FILE, "r+b") as f:
    map_file = mmap.mmap(f.fileno(), 0, prot=mmap.PROT_READ)
    for line in iter(map_file.readline, b""):
        # whatever

请注意,在A/63/13中,iter(>>的发送inel para amount of by,而在A/63/12中,它需要成为<<>>/code>(即>>>>,而不是b>>。

Answer 2


我修改了你的榜样:

with open(STAT_FILE, "r+b") as f:
        m=mmap.mmap(f.fileno(), 0, prot=mmap.PROT_READ)
        while True:
                line=m.readline()
                if line ==   : break
                print line.rstrip()


<>Suggestions:


Do not call a variable map, this is a built-in function.
Open the file in r+b mode, as in the Python example on the mmap help page. It states: In either case you must provide a file descriptor for a file opened for update. See http://docs.python.org/library/mmap.html#mmap.mmap.
It s better to not use UPPER_CASE_WITH_UNDERSCORES global variable names, as mentioned in Global Variable Names at https://www.python.org/dev/peps/pep-0008/#global-variable-names. In other programming languages (like C), constants are often written all uppercase.


希望这一帮助。

Edit: I did some timing tests on Linux because the comment made me curious. Here is a comparison of timings made on 5 sequential runs on a 137MB text file.

普通档案查阅:

real    2.410 2.414 2.428 2.478 2.490
sys     0.052 0.052 0.064 0.080 0.152
user    2.232 2.276 2.292 2.304 2.320


 档案查阅:

real    1.885 1.899 1.925 1.940 1.954
sys     0.088 0.108 0.108 0.116 0.120
user    1.696 1.732 1.736 1.744 1.752


这些时间安排不包括<条码>说明(我除外)。 在这些数字之后,我可以说,用于查阅档案的记忆速度非常快。

<<>python -m cProfile test.py 我得出以下结果:

5432833    2.273    0.000    2.273    0.000 {method  readline  of  file  objects}
5432833    1.451    0.000    1.451    0.000 {method  readline  of  mmap.mmap  objects}


如果Im没有错,那么mmap就会更快。

此外,看来<代码>而不是len(line)的性能低于line =,至少是我如何解释简介员的产出。

Answer 3

下面是简明扼要的:

with open(STAT_FILE, "r") as f:
    m = mmap.mmap(f.fileno(), 0, prot=mmap.PROT_READ)
    while True:
        line = m.readline()  
        if line == "": break
        print line
    m.close()

Note that line retains the newline, so you might like to remove it. It is also the reason why if line == "" does the right thing (an empty line is returned as " ").

The reason the original iteration works the way it does is that mmap tries to look like both a file and a string. It looks like a string for the purposes of iteration.

我不知道它为什么可以提供(或选择不提供)<条形码>(<>>/条码>。

Answer 4

视窗上的灰色2.732倍以上是半衰期的快速:

在27MB,509k条线文字档案(我的传承功能并不令人感兴趣,大部分只是读线(非常快):

with open(someFile,"r") as f:
    if usemmap:
        m=mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ)
    else:
        m=f
        e.parse(m)

With MMAP:

read in 0.308000087738

没有微额信贷计划:

read in 0.680999994278

Answer 5

如果你误用<条码>mmap(>):

with open( /content/drive/MyDrive...... , "r+b") as f:
    # map_file = mmap.mmap(f.fileno(), 0, prot=mmap.PROT_READ) as mmap not recogn. import something
    for line in iter(f.readline, b""):
      print(line)

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