Python - function 调用 exec() 看不到变量

Question

I have following script that works well on it's own, but once I wrap it all into a function does not return data. The command changes based on input data structure. This is an example of the command I want to feed into the exec():

cross_data=pd.crosstab(src_data['result'],[src_data['c1'],src_data['c2']],normalize='index')

This is my function I want to wrap the code in and call:

    def calcct(file_path='src_data.csv', separator = ",", res_col = 'result'):    
        #define function

        src_data = csv_import(file_path, separator) #import data
        reorder_cols = reorder_columns(src_data, res_col) #work with data
        head_list=list(reorder_cols.columns.values) #get dataframe headers

        # create command based on headers and execute that. Should return dataframe called cross_data.
        exec(crosstabcmd(head_list)) 
        return cross_data

Results in:

NameError: name 'cross_data' is not defined

I cannot seem to find the correct syntax for calling exec inside a function. I tried defining and passing the cross_data variable, but I just get an error it doesnt see pandas when I do that.

Or is there some better way? I need to compose the command of 2-x column names, count and names of columns are variable.

Answer 1

First up

You probably don't mean to be using exec - that's a pretty low-level functionality. There isn't really enough context to understand how to fix this yet. Could you write out (in your question) what the crosstabcmd function looks like?

The error

NameError: name 'cross_data' is not defined

is because you've never defined a variable called cross_data in the scope of function calcct , ie you have never done cross_data = "something" .

I'll give it a go

Assuming you have something like

import pandas as pd

def crosstabcmd(head_list):
    # ? I can only guess what your crosstabcmd does, this won't work though
    return pd.crosstab(*head_list, normalize='index')

then the solution would look like:

def calcct(file_path = 'src_data.csv', separator = ",", res_col = 'result'):
    src_data = csv_import(file_path, separator) #import data
    reorder_cols = reorder_columns(src_data, res_col) #work with data
    head_list=list(reorder_cols.columns.values) #get dataframe headers
    cross_data = crosstabcmd(head_list)
    return cross_data

Answer 2

In my case I had main script which called a second script. I needed to use the "c" variable within the second script. Therefore I used locals(),loc as arguments for exec().

loc = {}
a = 10
b = 5
def abc(a,b):
    qwerty = "c = %d + %d"%(a,b)
    exec(qwerty, locals(), loc)
    c = loc['c']
    d = c+2
    print(d)

abc(a,b)