counting number with 3 csvs python

Question

I have 3 csv that i will like to change one column to a running number that depends on the number on rows in the file. For exmaple, file 1 got 400 rows, file 2 got 240, and file 3 got 100. so the added column for file 1 will be running number from 1 to 400. so the added column for file 2 will be running number from 401 to 640. so the added column for file 3 will be running number from 641 to 741.

what I wrote is this

file1 = str(path) + "file1"
file2 = str(path) + "file2"
file3 = str(path) + "file3"
files = [file1, file2, file3]


class File_Editor():
    def line_len(self):
        for k in range(0,2):
            file_name = open(files[k] + ".csv")
            numline = len(file_name.readlines())
            print (numline)

I am stuck with making the running number for each file by remembering the number of row that were on the file before.

Thanks Alot!

+++++EDIT+++++

@roganjosh Thanks alot, I used your code with a little fixed for the running_number = 1, I have put it inside the def, that both files will have the same running number.

One last thing, How can I add at the first row Index, for example, "Number" and then from the 2nd row, run the running_number_in_csv.

Thanks

Answer 1

@roganjosh I have fixed my code. I know what is the lenght on the file, now i need to add a column with running numbers like:

file1 1 to 400

file2 401 to 641

file 3

642 to 742

Thanks alot!

Answer 2

Looking at your previous questions that are left open, the common theme is fundamental issue with understanding in how to use functions in Python that isn't being addressed. I will try and unpick part of this to prevent similar questions arising. I'm assuming you come from a scientific background like me so I'll stick to that.

You never pass arguments to your functions, only self . Instead you try to reference globals from within the function, but there is no need and it is confusing. For example, I might have the equation y = x^2 + 3x + 5 that is both a mathematical function and can be a python function.

def quadratic(value_of_x):
    y = (value_of_x **2) + (3*value_of_x) + 5
    return y

eg_1 = quadratic(5)
print (eg_1)
eg_2 = quadratic(3)
print (eg_2)

# But this will fail
#print (y)

y exists only within the Python function as a local variable and is destroyed once you leave the def / return block. In this case, eg_1 , eg_2 assume the value of y at the end of the function and value_of_x assumes the value that I put in brackets on the function call (the argument/variable). That's the point of functions, they can be used over and over.

I can also pass multiple arguments to the function.

def new_quadratic(value_of_x, coefficient):
    y = coefficient*(value_of_x **2) + (3*value_of_x) + 5
    return y

eg_3 = new_quadratic(5, 2)
print (eg_3)

Not only can I not get a value for y outside of the scope of a function, but a function does nothing unless it's called. This does nothing; it's the equivalent of knowing the formula in your head but never running a number through it - you're just defining it as something that your script could use.

starting_number = 5

def modify_starting_number(starting_number):
    starting_number = starting_number * 2
    return starting_number

print (starting_number)

Whereas this does what you expected it to do. You call the function ie pass the number through the formula.

starting_number = 5

def modify_starting_num(starting_num):
    starting_num = starting_num * 2
    return starting_num

starting_number = modify_starting_num(starting_number) # Calling the function
print (starting_number)

With that out of the way, on to your question.

import csv

files = ['file_1', 'file_2']

def running_number_in_csv(filename_list):
    """ running_number resets every time the function is called, but is 
    remembered within the function itself"""
    running_number = 1 

    for individual_file in filename_list:
        new_rows = [] # Make something to hold row + extra column

        # Read contents of each row and append the running number to the list
        with open(individual_file + '.csv', 'r') as infile:
             reader = csv.reader(infile)
             for row in reader:
                 row.append(running_number)
                 new_rows.append(row)
                 running_number += 1 # Increments every row, regardless of file name number

        # Write the list containing the extra column for running number
        with open(individual_file + '.csv', 'w') as outfile: # Might need 'wb' in Windows
            writer = csv.writer(outfile)
            writer.writerows(new_rows)

get_running_number = running_number_in_csv(files) # CALL THE FUNCTION :)