```
opened_file = open('AppleStore.csv')
from csv import reader
read_file = reader(opened_file)
apps_data = list(read_file)
def extract(data_set, index):
column = []
for row in data_set[1:]:
value = row[index]
column.append(value)
return column
def find_sum(a_list):
a_sum = 0
for element in a_list:
a_sum += float(element)
return a_sum
def find_length(a_list):
length = 0
for element in a_list:
length += 1
return length
def mean(data_set, index):
column = []
column = extract(data_set, index)
mean = find_sum(column)/find_length(column)
return mean
avg_price = mean(apps_data, 4)
print(avg_price)
```

I get the correct answer.

But I donâ€™t understand why I have to define a list in the â€śmean()â€ť function when there is a list defined in the â€śextract()â€ť function which the â€śmean()â€ť function refers to.

Cheers,

Christophe