Problems with importing list of data from python to csv

Question

I've just started using python, and I have some problems with exporting a list of data from python to csv.

I have some array of values, and each value corresponds to a specific time. What I want is copying these arrays (all have the same length) on a csv so that each row presents the value of all the variables for that specific instant of time. What I've written is:

with open ('Risultati.csv', 'w', newline='' ) as f:
    thewriter=csv.writer(f)
    
    thewriter.writerow(['x','y','z','w'])
    for i in range(0,len(x)):
        thewriter.writerow(['x[%i]', 'y[%i]','z[%i]','w[%i]'])

but in the csv I've obtained in each row is x[%i] y[%i] z[%i] w[%i] . I also would like that each list of values appears aligned with the header, like in a table with Excel.

I hope I made myself clear. Thank you in advance.

Answer 1

What about the following:

import csv
import random

x = random.sample(range(10, 30), 5)
y = random.sample(range(10, 30), 5)
z = random.sample(range(10, 30), 5)
w = random.sample(range(10, 30), 5)

with open ('out.csv', 'w', newline='' ) as f:
    thewriter=csv.writer(f)

    thewriter.writerow(['x','y','z','w'])
    for i in range(0,len(x)):
        thewriter.writerow([x[i], y[i], z[i], w[i]])

Gives you:

$ python3 ./test.py
$ cat ./out.csv
x,y,z,w
18,23,17,25
23,27,16,26
15,18,28,10
12,15,23,18
26,29,21,27

I would strongly recommend you read a tutorial on python lists, There are many out there, for example this one

Answer 2

Wouldn't it be possible to create pandas Dataframe and then save it to file at once? Small example below:

import pandas as pd

# buffer for data
values = []
# here adding exemplary rows
values.append({'x':1, 'y':2, 'z':3, 'w':4})
values.append({'x':4, 'y':5, 'z':6, 'w':7})
# convert to df
df = pd.DataFrame(values)
# save to csv
df.to_csv('file.csv', index=None)

Answer 3

The comment from @urban to the original post seems correct.

Still, I would advise you to take a look at the Pandas library (you will probably be using it at some point anyways). You would only need:

import pandas as pd
df = pd.DataFrame()  # create a new empty DataFrame
df['x'] = x  # fill it with values
df['y'] = y
df['z'] = z
df['w'] = w
df.to_csv('.../file.csv', index=None)

Pandas also lets you use df.to_excel() , df.to_parquet() , and more, to save your output in other file formats.