[英]Different results achieved using Python's os.walk function and ls command
#!/bin/python
import os
pipe=os.popen("ls /etc -alR| grep \"^[-l]\"|wc -l") #Expr1
a=int(pipe.read())
pipe.close()
b=sum([len(files) for root,dirs,files in os.walk("/etc")]) #Expr2
print a
print b
print "a equals to b ?", str(a==b) #False
print "Why?"
What is the difference between Expr1 's function and Expr2 's? Expr1的功能和Expr2的功能有什么区别 ? I think Expr1 gives the right answer, but not sure. 我认为Expr1提供正确的答案,但不确定。
Short answer: 简短答案:
ls -laR | grep "^[-l]"
ls -laR | grep "^[-l]"
counts symlinks to directories. ls -laR | grep "^[-l]"
计算到目录的符号链接。 It matches any line that begins with l
and that includes symlinks to directories. 它与任何以l
开头并且包括目录符号链接的行匹配。
In contrast, [files for root, dirs, files in os.walk('/etc')]
does not count symlinks to directories . 相反, [files for root, dirs, files in os.walk('/etc')]
不计入目录的符号链接 。 It ignores all directories and lists only files. 它忽略所有目录,仅列出文件。
Long answer: 长答案:
Here is how I identified the discrepancies: 这是我识别差异的方法:
import os
import subprocess
import itertools
def line_to_filename(line):
# This assumes that filenames have no spaces, which is a false assumption
# Ex: /etc/NetworkManager/system-connections/Wired connection 1
idx = line.rfind('->')
if idx > -1:
return line[:idx].split()[-1]
else:
return line.split()[-1]
line_to_filename
tries to find the filename in the output of ls -laR
. line_to_filename
尝试在ls -laR
的输出中找到文件名。
This defines expr1
and expr2
and is essentially the same as your code. 这定义了expr1
和expr2
并且与您的代码基本相同。
proc=subprocess.Popen(
"ls /etc -alR 2>/dev/null | grep -s \"^[-l]\" ", shell = True,
stdout = subprocess.PIPE) #Expr1
out, err = proc.communicate()
expr1 = map(line_to_filename, out.splitlines())
expr2 = list(itertools.chain.from_iterable(
files for root,dirs,files in os.walk('/etc') if files)) #Expr2
for expr in ('expr1', 'expr2'):
print '{e} is of length {l}'.format(e = expr, l = len(vars()[expr]))
This removes names from expr1
that are also in expr2
: 这将从expr1
中删除也位于expr2
中的名称:
for name in expr2:
try:
expr1.remove(name)
except ValueError:
print('{n} is not in expr1'.format(n = name))
After removing filenames that expr1
and expr2
share in common, 删除expr1
和expr2
共同共享的文件名后,
print(expr1)
yields 产量
['i386-linux-gnu_xorg_extra_modules', 'nvctrl_include', 'template-dkms-mkdsc', 'run', '1', 'conf.d', 'conf.d']
I then used find
to find these files in /etc
and tried to guess what was unusual about these files. 然后,我使用find
在/etc
找到这些文件,并试图猜测这些文件的异常之处。 They were symlinks to directories (rather than files). 它们是目录(而不是文件)的符号链接。
On my machine, /etc is a symlink to /private/etc, so ls /etc
has only one line of output. 在我的机器上,/ etc是/ private / etc的符号链接,因此ls /etc
只有一行输出。 ls /etc/
give the expected equivalence between ls
and os.walk
. ls /etc/
给出了ls
和os.walk
之间的等效值。
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