Python For Loop Appending Only Last Value to List

Question

I have a loop that is setting the values of one list to the value of another and while I am able to achieve this with my current code it is only appending the last grouping of values to my list. What could possibly be off in my setup that could cause this behavior?

Here is my data format:

print(df_full_raw_format) # Data Set being set to worksheet_range values

<class 'pandas.core.frame.DataFrame'>
     b_clicks  b_cpc  date_string
0    b_clicks  b_cpc  date_string
1          72   2.43   2018-01-01
2         232    2.8   2018-01-02
3         255    2.6   2018-01-03
4         249   2.65   2018-01-04
5         202   2.86   2018-01-05

Here is my worksheet_range format:

[<Cell R1C1 ''>, <Cell R2C1 ''>, <Cell R3C1 ''>,....]

Here is my function with the for loops:

update_raw_data_sheet(df_full_raw_format)

def update_raw_data_sheet(data_set):
    for col_val, col_name in zip(gs_columns, columns):
        updated_values = [] # List storing the combined list values
        column_data = data_set[col_name].values.tolist(); # col_name = ['b_clicks', 'b_cpc', 'date_string']
        print("COLUMN DATA")
        print(column_data)
        worksheet_range = worksheet.range(1, col_val, len(column_data), col_val); # [row_start, col_start, row_end, col_end]
        print(worksheet_range)
        for cell, data in zip(worksheet_range, column_data):
            cell.value = data # <Cell R1C1 '2018-01-01'>...
            print(cell)
            updated_values.append(cell)

    print(updated_values)

Here is the console:

(Loop 1)
COLUMN DATA
['date_string', '2018-01-01', '2018-01-02', '2018-01-03', ...] # print(column_data)
[<Cell R1C1 ''>, <Cell R2C1 ''>, <Cell R3C1 ''>,...] # print(worksheet_range)
<Cell R1C1 'date_string'> # print(cell)
<Cell R2C1 '2018-01-01'>
<Cell R3C1 '2018-01-02'>
<Cell R4C1 '2018-01-03'>
... (Loop 2)
COLUMN DATA
['b_clicks', '72', '232', '255', ...]
[<Cell R1C2 ''>, <Cell R2C2 ''>, <Cell R3C2 '', ...]
<Cell R1C2 'b_clicks'>
<Cell R2C2 '72'>
<Cell R3C2 '232'>
... (Loop 3)
COLUMN DATA
['b_cpc', 2.43, 2.8,...]
[<Cell R1C3 'b_cpc'>, <Cell R2C3 '2.43'>, <Cell R3C3 '2.8'>, ...]
<Cell R1C3 'b_cpc'>
<Cell R2C3 2.43>
<Cell R3C3 2.8>
(Post-Loop)
[<Cell R1C3 'b_cpc'>, <Cell R2C3 2.43>, <Cell R3C3 2.8>, ...] # print(updated_values)

It misses the first two loops worth of values, but perfectly captures the 3rd in the array.

Does this answer your question? [How can I collect the results of a repeated calculation in a list, dictionary etc. (or make a copy of a list with each element modified)?](https://stackoverflow.com/questions/75666408/how-can-i-collect-the-results-of-a-repeated-calculation-in-a-list-dictionary-et) — mkrieger1, Apr 17 '23 at 10:29

score 4 · Accepted Answer · answered Dec 14 '18 at 17:29

4

updated_values = []

should be outside loop just after def statement, otherwise you overwrite values added to the list in every iteration.

def update_raw_data_sheet(data_set):
    updated_values = []
    # ...

answered Dec 14 '18 at 17:29

Austin

25,759
4
25
48

score 0 · Answer 2 · answered Dec 14 '18 at 17:31

This is exactly what you programmed. You reset updated_values on each iteration of the outer loop, which wipes out the previous values:

for col_val, col_name in zip(gs_columns, columns):
    updated_values = [] # List storing the combined list values

If you want all three iterations` of data, then you need to lift the initialization out of the loop:

updated_values = [] # List storing the combined list values
for col_val, col_name in zip(gs_columns, columns):

Python For Loop Appending Only Last Value to List

2 Answers2

Linked

Related