Exec function won't work in Python with a pandas dataframe

Question

I have an initial dataframe called source_data.

I have a separate text file which allows a user to place some python code in for some filter criteria. I know this is seen as bad practice, but my company has assured me that it's safe to do. I've noted my concerns but I have the green light.

So, this CSV has this string in a cell: source_data.loc[source_data['CONFIG_ID'] == 3]

This is read in as a list. As an example, here's two prints:

print('Number of where clause conditions found: ' + str(len(segmentFilterCriteria)))
print('Where clause criteria: ' + str(segmentFilterCriteria))

Console shows:

Number of where clause conditions found: 1
Where clause criteria: ["source_data.loc[source_data['CONFIG_ID'] == 3]"]

Now, when I run this (i.e. using the text string and the exec function), my base_data dataframe appears as NoneType:

print(segmentFilterCriteria[0])
base_data = exec(segmentFilterCriteria[0])
print(base_data.columns)

Console shows:

source_data.loc[source_data['CONFIG_ID'] == 3]
Traceback (most recent call last):

  File "<ipython-input-95-17bc7d85852e>", line 3, in <module>
    print(base_data.columns)

AttributeError: 'NoneType' object has no attribute 'columns'

However, when I just type the code out, like this, it works fine:

base_data = source_data.loc[source_data['CONFIG_ID'] == 3]
print(base_data.columns)

Console shows:

Index(['CONFIG_ID', 'ACCOUNT_DEAL_ID', 'FACILITY_ID',
       'M12_PD_INITIAL_RECOG_VAL',
...

Why does my string executed inside an exec function not work in this case?

Roman L · Accepted Answer · 2018-04-05 14:55:31Z

3

exec() function doesn't return any result. It always returns None. You should use it like this:

print(segmentFilterCriteria[0])
exec('base_data=' + segmentFilterCriteria[0])
print(base_data.columns)

answered Apr 5, 2018 at 14:55

Roman L

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