CODEWITHSUNDEEP
pythonpandas
noobie
noobie

Reputation: 2607

Appending data to Pandas global dataframe variable does not persist

I am trying to use a pandas dataframe global variable. However, the dataframe is empty when I try to reassign or append it to the global variable. Any help appreciated.

import pandas as pd

df = pd.DataFrame()

def my_func():

    global df

    d = pd.DataFrame()

    for i in range(10):
        dct = {
            "col1": i,
            "col2": 'value {}'.format(i)    
        }

        d.append(dct, ignore_index=True) 
        # df.append(dct, ignore_index=True) # Does not seem to append anything to the global variable
    df = d # does not assign any values to the global variable

my_func()

df.head()

Upvotes: 1

Views: 709

Answers (1)

Chris
Chris

Reputation: 29742

As opposed to list.append, pandas.DataFrame.append is not an in-place operation. Slightly changing your code works as expected:

import pandas as pd

df = pd.DataFrame()

def my_func():
    global df
    d = pd.DataFrame()
    for i in range(10):
        dct = {
            "col1": i,
            "col2": 'value {}'.format(i)}
        d = d.append(dct, ignore_index=True) # <<< Assignment needed
        # df.append(dct, ignore_index=True) # Does not seem to append anything to the global variable
    df = d # does not assign any values to the global variable

my_func()

df.head()

Output:

   col1     col2
0   0.0  value 0
1   1.0  value 1
2   2.0  value 2
3   3.0  value 3
4   4.0  value 4

Upvotes: 2

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