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I am quite new to python and currently trying to work on a project that asks the user to read data from a csv file, and to store that data so that other functions can be performed on it. The only issue I seem to be having at the moment is that I can't use global variables.

Just now I have the following code structure:

import csv
import sys
data_set = []

def loadFile(x):
    with open(x, "r") as readfile:
        csv_reader = csv.reader(readfile, delimiter= ';')
        for row in csv_reader:
            data_set.append(row)
    print("Loaded weather data from", (x[0:-4]).capitalize())
    print()

def avgDay(x):
    for line in data_set:
        if(len(x) == 5 and (x[3:5] + "-" + x[0:2]) in line[0]):
           print("The weather on", x, "was on average", line[2], "centigrade")

Is there some way I can call data_set to other functions? (I have a few more functions that need to work with the data).

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9
  • Is there a main starting point ? Commented May 9, 2020 at 15:49
  • 2
    other_function(data_set)…‽ Commented May 9, 2020 at 15:49
  • Just use function arguments and return values. loadFile can return the data in a list, and avgDay could take that data as an argument. Commented May 9, 2020 at 15:50
  • What do you mean by can't use global variables? Does it throw an error when you try to use it? Also, you could always encapsulate the functions and data into a class... that way you can use self to get the data. Commented May 9, 2020 at 15:51
  • List is an object. Though it's reference is passed by value, the content can be shared between functions. Commented May 9, 2020 at 15:52

4 Answers 4

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4

Yes, simply pass it in as a parameter, and return it when it is originally generated.

import csv
import sys

def loadFile(x):
    date_set = []
    with open(x, "r") as readfile:
        csv_reader = csv.reader(readfile, delimiter= ';')
        for row in csv_reader:
            data_set.append(row)
    print("Loaded weather data from", (x[0:-4]).capitalize())
    print()
    return data_set

def avgDay(x, data_set):
    for line in data_set:
        if(len(x) == 5 and (x[3:5] + "-" + x[0:2]) in line[0]):
           print("The weather on", x, "was on average", line[2], "centigrade")

def main():
    data_set = loadFile(...)
    avgDay(..., data_set)

if __name__ == 'main':
    main()
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5 Comments

Thank you, lecturer was just saying no using global variables and pointed me to a very basic tutorial on parameters but couldn't figure out how that would work in my code without the above example.
Ok looks like I spoke too soon, I am getting a data_set not defined error when using this method, but that's because I am not using a main, I am using the following format for returning my functions. def menu_number(): number = int(input("Choose what to do: ")) if (number) == 1: x = input("Give name of the file: " ) loadFile(x) print_menu() menu_number() elif (number) == 2: x = input("Give a date (dd.mm): ") avgDay(x, data_set) lowHigh(x, data_set) rain(x, data_set)
@AlexanderKerr Sorry, you will have to ask a new question on the site, it is too hard to debug in comments.
Will do, I had prev thought to, then deleted since I had this here.
Posted new question and put full code up, question is @ stackoverflow.com/questions/61828948/… , would appreciate your input on where I went wrong with it please?
1

Your loadFile function can return a dataset that can be used inside avgDay

import csv
import sys


def loadFile(x):

    data_set = []

    with open(x, "r") as readfile:
        csv_reader = csv.reader(readfile, delimiter= ';')
        for row in csv_reader:
            data_set.append(row)
    print("Loaded weather data from", (x[0:-4]).capitalize())
    print()

    return data_set

def avgDay(x):

    data_set = loadFile(x)

    for line in data_set:
        if(len(x) == 5 and (x[3:5] + "-" + x[0:2]) in line[0]):
           print("The weather on", x, "was on average", line[2], "centigrade")
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Comments

0

global vars can only be set if u use the word global

you can access global vars without anything special

data_set = "global_var" #global

def print_global_data_set():
    print(data_set)

def set_global_data_set():
    global data_set # you need this line to tell python that you are going to set a global variable
    data_set = 'global_var_set_from_function'

def set_local_data_set():
    data_set = "local" # this will not set the global var but a local var so the global data_set stays unchanged

print(data_set) # outputs "global_var"
set_local_data_set()
print_global_data_set() # outputs "global_var" (set_local_data_set did not set the global var but a local var)
set_global_data_set()
print_global_data_set() # outputs "global_var_set_from_function"
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1 Comment

That statement isn't quite true though is it? If I define a variable outside the scope of a function, that variable is automatically assigned a global status.
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Functions can have attributes. You can make data_set an attribute of loadFile and then reference it in avgDay. 

with open(x, "r") as readfile:

    csv_reader = csv.reader(readfile, delimiter= ';')

    for row in csv_reader:

        data_set.append(row)

    loadFile.data_set_attr = data_set

Then, in avgDay, reference loadFile.data_set_attr

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1 Comment

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