Python read text file columnwise

[Avi Gross]

-----Original Message-----
From: Avi Gross <avigross at verizon.net> 
Sent: Saturday, January 12, 2019 8:26 PM
To: 'DL Neil' <PythonList at DancesWithMice.info>
Subject: RE: Python read text file columnwise

I am not sure what the big deal is here. If the data is consistently
formatted you can read in a string per line and use offsets as in line[0:8]
and so on then call the right transformations to comvert them to dates and
so on. If it is delimited by something consistent like spaces or table or
commas, we have all kinds of solutions ranging from splitting the line on
the delimiter to using the kind of functionality that reads in such files
into a pandas DataFrame.

In the latter case, you get the columns already. In the former, there are
well known ways to extract the info such as:

[row[0] for row in listofrows]

And repeat for additional items.

Or am I missing something and there is no end of line and you need to read
in the entire file and split it into size N chunks first? Still fairly
straightforward.

-----Original Message-----
From: Python-list <python-list-bounces+avigross=verizon.net at python.org> On
Behalf Of DL Neil
Sent: Saturday, January 12, 2019 4:48 PM
To: python-list at python.org
Subject: Re: Python read text file columnwise

On 12/01/19 1:03 PM, Piet van Oostrum wrote:
> shibashibani at gmail.com writes:
> 
>> Hello
>>>
>>> I'm very new in python. I have a file in the format:
>>>
>>> 2018-05-31	16:00:00	28.90	81.77	4.3
>>> 2018-05-31	20:32:00	28.17	84.89	4.1
>>> 2018-06-20	04:09:00	27.36	88.01	4.8
>>> 2018-06-20	04:15:00	27.31	87.09	4.7
>>> 2018-06-28	04.07:00	27.87	84.91	5.0
>>> 2018-06-29	00.42:00	32.20	104.61	4.8
>>
>> I would like to read this file in python column-wise.
>>
>> I tried this way but not working ....
>>    event_list = open('seismicity_R023E.txt',"r")
>>      info_event = read(event_list,'%s %s %f %f %f %f\n');


To the OP:

Python's standard I/O is based around data "streams". Whilst there is a
concept of "lines" and thus an end-of-line character, there is not the idea
of a record, in the sense of fixed-length fields and thus a defining and
distinction between data items based upon position.

Accordingly, whilst the formatting specification of strings and floats might
work for output, there is no equivalent for accepting input data. 
Please re-read refs on file, read, readline, etc.


> Why would you think that this would work?

To the PO:

Because in languages/libraries built around fixed-length files this is how
one specifies the composition of fields making up a record - a data
structure which dates back to FORTRAN and Assembler on mainframes and other
magtape-era machines.

Whilst fixed-length records/files are, by definition, less flexible than the
more free-form data input Python accepts, they are more efficient and faster
in situations where the data (format) is entirely consistent
- such as the OP is describing!


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Regards =dn
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