Check for non-floats in a csv file python3

Question

I'm trying to read a csv file, and create a 2 dimensional list from the values stored inside.

However I'm running into trouble when I try to check whether or not the values stored can be converted into floats.

Here is the function I have written, which reads the file and creates a list.

def readfile(amount, name):
    tempfile = open(name).readlines()[1:]    #First value in line is never a float, hence the [1:]
    rain_list = []
    count = 0.0
    for line in tempfile:            
        line = line.rstrip()
        part = line.split(",")
        try:
            part = float(part)
        except ValueError:
            print("ERROR: invalid float in line: {}".format(line))
        rain_list.append(part[amount])
        count += 1
    if count == 0:
         print("ERROR in reading the file.")
    tempfile.close()
    return rain_list

It might be a little messy, since it's essentially a patchwork of different possible solutions I have tried.

The values it gets are the name of the file (name) and the amount of values it reads from the file (amount).

Has anyone got an idea why this does not work as I expect it to work?

Jean-François Fabre · Accepted Answer · 2018-11-06 12:25:52Z

2

part is a list of strings. To check & convert for all floats, you'd have to do:

part = [float(x) for x in part]

(wrapped in your exception block)

BTW you should use the csv module to read comma-separated files. It's built-in. Also using enumerate would allow to be able to print the line where the error occurs, not only the data:

reader = csv.reader(tempfile)  # better: pass directly the file handle
# and use next(reader) to discard the title line
for lineno,line in enumerate(reader,2):  # lineno starts at 2 because of title line
    try:
        line = [float(x) for x in line]
    except ValueError:
        print("ERROR: invalid float in line {}: {}".format(lineno,line))

edited Nov 6, 2018 at 12:25

answered Nov 6, 2018 at 12:21

Jean-François Fabre♦

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2 Comments

Astudent Over a year ago

Thanks, I haven't got any experience with the csv module yet, I'll have to check it out. When you say wrapped in your exception block, what do you mean by that?

Jean-François Fabre Over a year ago

I mean: like you did before. I have added a code snippet which uses csv

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