inplace text filter - without writing file
MRAB
python at mrabarnett.plus.com
Sun Oct 2 14:22:37 EDT 2016
On 2016-10-02 06:33, Sayth Renshaw wrote:
> On Sunday, 2 October 2016 16:19:14 UTC+11, Sayth Renshaw wrote:
>> On Sunday, 2 October 2016 12:14:43 UTC+11, MRAB wrote:
>> > On 2016-10-02 01:21, Sayth Renshaw wrote:
>> > > Hi
>> > >
>> > > I have a fileobject which was fine however now I want to delete a line from the file object before yielding.
>> > >
>> > > def return_files(file_list):
>> > > for filename in sorted(file_list):
>> >
>> > When joining paths together, it's better to use 'os.path.join'.
>> >
>> > > with open(dir_path + filename) as fd:
>> > > for fileItem in fd:
>> > > yield fileItem
>> > >
>> > > Ned gave an answer over here http://stackoverflow.com/a/6985814/461887
>> > >
>> > > for i, line in enumerate(input_file):
>> > > if i == 0 or not line.startswith('#'):
>> > > output.write(line)
>> > >
>> > > which I would change because it is the first line and I want to rid <!--
>> > >
>> > > for i, line in enumerate(input_file):
>> > > if line.startswith(<!--'):
>> > > output.write(line)
>> > >
>> > > However I do not want to write the file I want to restore all the enumerated files back to the fileItem I need to yield.
>> > >
>> > > How do I do this?
>> > >
>> > You use the logic of the answer from StackOverflow in your
>> > 'return_files' function:
>> >
>> > def return_files(file_list):
>> > for filename in sorted(file_list):
>> > with open(dir_path + filename) as fd:
>> > for fileItem in fd:
>> > if keep_item(fileItem):
>> > yield fileItem
>> >
>> >
>> > If you need to know the line number when deciding whether to keep a
>> > line, use enumerate too:
>> >
>> > def return_files(file_list):
>> > for filename in sorted(file_list):
>> > with open(dir_path + filename) as fd:
>> > for i, fileItem in enumerate(fd):
>> > if keep_item(fileItem, i):
>> > yield fileItem
>>
>> I just can't quite get it.
>>
>> def return_files(file_list):
>> for filename in sorted(file_list):
>> file = os.path.join(dir_path, filename)
>> print(file)
>> with open(file) as fd:
>> print(fd)
>> for fileItem in fd:
>> print(fileItem)
>> for line in fileItem:
>> print(line[0])
>> if line.startswith('<!--'):
>> print(line[1:])
>> yield line[1:]
>> else:
>> yield line[:]
>>
>> I maybe over baking it but just not getting it right.
>>
>> Sayth
>
> Aargh, half solved it, now it works except I am creating a list as the yielded item and lxml doesn't accept list it wants the file.
>
> def return_files(file_list):
> """
> Take a list of files and return file when called.
>
> Calling function to supply attributes
> """
> for filename in sorted(file_list):
> file = os.path.join(dir_path, filename)
> with open(file, 'r') as fd:
> data = fd.read().splitlines(True)
> if data[0].startswith('<!--'):
> print(data[1:])
> yield data[1:]
> else:
> yield data[0:]
>
A shorter way of reading the lines is:
lines = fd.readlines()
You can yield the lines one at a time with:
yield from lines
This is equivalent to:
for line in lines:
yield line
but is shorter, quicker and doesn't use a variable!
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