[Tutor] Reading a CSV file

[John Weller]

Many thanks to all who replied.  I hoped it would be something like a
dictionary.  The docs say that a dictionary is a sequence of key pairs -
key:value but it appears that the value can be several fields.  Is this the
case?

This program is intended to run 24/7 getting data every 10 minutes and using
it to control equipment dependent on whether it is day or night.  There will
be a setup function and a loop function.  I assume I can put the first part
to create the dictionary is setup and the call in the loop?

Thanks again

John

John Weller
01380 723235
07976 393631

-----Original Message-----
From: Tutor <tutor-bounces+john=johnweller.co.uk at python.org> On Behalf Of
David Rock
Sent: 12 June 2020 23:43
To: tutor at python.org
Subject: Re: [Tutor] Reading a CSV file

* John Weller <john at johnweller.co.uk> [2020-06-12 18:59]:
> I have a CSV file with 366 rows each with 4 comma separated fields; 
> day_no, date, sunrise, sunset.  The top row contains the field names.  
> I want access the time of sunrise and sunset from file for a particular
day_no.
> 
>  
> 
> I have tried:
> 
>  
> 
> import csv
> 
> with open('sun_times_gmt.csv', newline= '') as csvfile:
>     sun_times = csv.DictReader(csvfile, delimiter=',')
>     for row in sun_times:
>         print(row['sunrise'])
> 
> 
> but it prints out the entire column.  How do I specify a particular row?

This is because you are telling it to print every row.  You need to add an
if statement that prints only if day_no matches the entry you want.
For example:

with open('sun_times_gmt.csv', newline= '') as csvfile:
    sun_times = csv.DictReader(csvfile, delimiter=',')
    for row in sun_times:
        if row['day_no'] == 'your day_no value here':
            print(row['sunrise'])


You could also play around with using the value of day_no to be a key for
the data so you can access it more directly.  If day_no is unique, you can
do this:

days = {}
with open('sun_times_gmt.csv', newline= '') as csvfile:
    sun_times = csv.DictReader(csvfile, delimiter=',')
    for row in sun_times:
        days[row['day_no']] = row

print(days['your day_no value here']['sunrise'])


It depends on exactly how you want to reference the data later

--
David Rock
david at graniteweb.com
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