<p>替换文件行的(相对)安全的方法。</p>
<pre><code>#!/usr/bin/python
# defensive programming style
# function to replace a line in a file
# and not destroy data in case of error
def replace_line(filepath, oldline, newline ):
"""
replace a line in a temporary file,
then copy it over into the
original file if everything goes well
"""
# quick parameter checks
assert os.exists(filepath) # !
assert ( oldline and str(oldline) ) # is not empty and is a string
assert ( newline and str(newline) )
replaced = False
written = False
try:
with open(filepath, 'r+') as f: # open for read/write -- alias to f
lines = f.readlines() # get all lines in file
if oldline not in lines:
pass # line not found in file, do nothing
else:
tmpfile = NamedTemporaryFile(delete=True) # temp file opened for writing
for line in lines: # process each line
if line == oldline: # find the line we want
tmpfile.write(newline) # replace it
replaced = True
else:
tmpfile.write(oldline) # write old line unchanged
if replaced: # overwrite the original file
f.seek(0) # beginning of file
f.truncate() # empties out original file
for tmplines in tmpfile:
f.write(tmplines) # writes each line to original file
written = True
tmpfile.close() # tmpfile auto deleted
f.close() # we opened it , we close it
except IOError, ioe: # if something bad happened.
printf ("ERROR" , ioe)
f.close()
return False
return replaced and written # replacement happened with no errors = True
</code></pre>
<p>(注意:这只替换整行,以及文件中匹配的所有行)</p>