[Tutor] how to read from a txt file

[Brian van den Broek]

jrlen balane said unto the world upon 2005-02-13 11:49:
> guys, how would i do this: 
> i want to read from a text file
> the text file should contain should contain data (say, decimal value
> from 1-1200). there should be no other type of entry but decimal
> it should contain 96 data all in all, with each data separated by a
> comma or each data is numbered from 1-96 (or better yet, any
> suggestions on this???)

Hi,

So, you have control over the creation of the data file, too? Is it 
being created by a Python process? If so, pickling your data might 
make more sense. If the data was generated by a class with each data 
point stored as a class attribute, for instance, you could just pickle 
the class. Does this sound possible in your situation?

> now, the program should read each data every 5 minutes for eight hours
> the data will be sent to the serial port and will be executed by an
> external hardware. the serial part is ok, and the problem now is how
> to read from a text file.
> any help, pls.
> 
> what i know (chapter 7 of the tutorial):
> 1) first, to open a txt file, i can use open() say:
>                 f = open(*.txt, r)
> a user can use the notepad to create the text file so i'll just open
> it for reading. my problem now would be on reading the contents of the
> file.
> 2) f.read(size), since my data ranges from 0-1200, size = 2 for each read.
> 3) should i do this:
>        for data in range (1, 96,1):
>             f.read(2)
>             ...
>             time.sleep(300) # 5 minutes
> 4) since f.read() returns string, how would i convert this back to
> decimal value, since i would need the decimal value for the serial
> part.

Since you files are quite short, I'd do something like:

<code>
data_file = open(thedata.txt, 'r') # note -- 'r' not r
data = data_file.readlines()       # returns a list of lines

def process(list_of_lines):
     data_points = []
     for line in list_of_lines:
         data_points.append(int(line))
     return data_points

process(data)
</code>

This assumes that each line of the data file has nothing but a string 
with an int followed by '\n' (for end of line), and that all you need 
is a list of those integers. Maybe these are bad assumptions -- but 
they might get you started.

HTH,

Brian vdB