Pandas Data Frame, reading from a file or setting a new Data Frame inside a function

Question

I am trying to read 3 CSV files into 3 pandas DataFrame. But after executing the function the variable seems not available. Tries to create a blank data frame outside the function and read and set the frame in the function. But the frame is blank.

# Load data from the csv file
def LoadFiles():
    x = pd.read_csv('columns_description.csv', index_col=None)
    print("Columns Description")
    print(f"Number of rows/records: {x.shape[0]}")
    print(f"Number of columns/variables: {x.shape[1]}")
    
LoadFiles()
x.head()

Python Notebook for above code with Error

In the second approach, I am trying to create a new data frame with some consolidated information from the dataset. The issue reappears as the variable seems to be no longer available.

# Understand the variables
y = pd.read_csv('columns_description.csv', index_col=None)

def refresh_y():
    var_y = pd.DataFrame(columns=['Variable','Number of unique values'])
    for i, var in enumerate(y.columns):
        var_y.loc[i] = [y, y[var].nunique()]
        
refresh_y()

Screenshot with error code and solution restructuring in the function

I am a bit new to Python, The code is a sample and does not represent actual data and in the function, an example is with a single column. I have multiple columns to refresh in this derived data set based on changes further hence the function approach.

your functions should return the desired dataframes (and possibly take file name and `y` as argument respectively) — Tranbi, Nov 20 '21 at 07:47

Savvas · Answer 1 · 2021-11-20T21:29:40.063

0

When defining a function, if you want to use a variable that is defined in the function, you should end with return var. Check this: Function returns None without return statement and some tutorials on defining a function (https://learnpython.com/blog/define-function-python/).

A basic example to help you start with defining functions:

def sum_product(arg1,arg2): #your function takes 2 arguments
    var1 = arg1 + arg2
    var2 = arg1*arg2
    return var1,var2 #returns two values
new_var1, new_var2 = sum_product(3,4)

For the first example try modifying it like:

def LoadFiles():
    var = pd.read_csv('columns_description.csv', index_col=None)
    print("Columns Description")
    print(f"Number of rows/records: {var.shape[0]}")
    print(f"Number of columns/variables: {var.shape[1]}")
    return var

x = LoadFiles()
x.head()

edited Nov 20 '21 at 21:29

answered Nov 20 '21 at 08:01

Savvas

1
2

I will try this out and update you. How do you handle multiple returns in function in python. I want to be able to read 3 or more files to 3 different frames. – Dilip M Nair Nov 20 '21 at 13:27
Check my edited answer. Additionally, following @Tranbi suggestion, it would be helpful to have y and filename as arguments for the function. – Savvas Nov 20 '21 at 21:38

score 0 · Answer 2 · answered Nov 24 '21 at 02:21

try following code

# Load data from the csv file
def LoadFiles():
    x = pd.read_csv('columns_description.csv', index_col=None)
    print("Columns Description")
    print(f"Number of rows/records: {x.shape[0]}")
    print(f"Number of columns/variables: {x.shape[1]}")
    return x
    
x2 = LoadFiles()
x2.head()

Variables in a function is only available inside function. You may need study about scope. I recommend the following simple site about scope in Python.

https://www.w3schools.com/python/python_scope.asp

Pandas Data Frame, reading from a file or setting a new Data Frame inside a function

2 Answers2