increment integer in python

Question

I wrote a simple function to read a file line by line, do some calculation and store the results in another file. However, when I output count in my function, instead of 0, 1, 2, 3; it becomes 6.21263888889e-05, 0.000141933611111, etc. I'm wondering what is the reason.

def CumulativePerSecond(input_file):
  # Record cumulative battery per second
  freq = 1000 # number of samples per second
  output_file = os.path.splitext(input_file)[0] + "_1s" + ".txt"
  output = open(output_file, 'a+')
  count = 0
  for line2 in fileinput.input(input_file):
    count = count + 1
    print count
    if count == freq:
        output.write(str(line2))
        count = 0
  output.close()

Parts of Output:

1.87317876361

1.87321708889

1.87325520083

1.87329356889

1.87333199389

1.87337076056

1.87340823167

1.87344365278

1.87347473167

1.87351439528

1.87354390806

1.87362505778

Have you tried typecasting as an int (i.e. count = int(count + 1))? — Michael Molter
– Michael Molter, Commented Jul 1, 2016 at 16:26
Also, can you post more numbers in the series it produces, that give a little more information about what is generating the error. — Michael Molter
– Michael Molter, Commented Jul 1, 2016 at 16:28
Also, is your main goal to simply output a file with every 1000th data point from input. That could be written much simpler, and you may not even need count at all. — Michael Molter
– Michael Molter, Commented Jul 1, 2016 at 16:31
I tried count = int(count + 1)) and it doesn't work. I will add more output. Yeah, my goal is to output every 1000th data. Could you please let me know if there are some simpler ways? — ZigZagZebra
– ZigZagZebra, Commented Jul 1, 2016 at 16:34

Michael Molter · Accepted Answer · 2016-07-01 16:48:53Z

I don't know the specifics of your application, but I would send the data to a list, and then use Python's slice notation to select every 1000th data point.

Try the following snippet.

data = range(100)
every_tenth = data[::10]

Also, you can eliminate the need to explicitly close files if you use the with keyword.

with open(filename) as f:
    data = f.readlines()

The following is your code re-written more 'Pythonically'--that is, it takes advantage of some of the shortcuts that Python offers you over C. You may have to fiddle with it a little to get it to run. I am not sure how you are handling your files.

 def CumulativePerSecond(filename, freq=1000):
    data = []
    with open(filename) as input_file:
        data = input_file.readlines()

    output_file = os.path.splitext(filename)[0] + "_1s.txt"
    with open(out_filename, 'a+') as output:
        for line in data[::freq]:
            output.write(line)

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