Why my loop always add the same value to my dictionnary in python?

July 1, 2022

I have this function that creates a dictionary from a list.
The code is truncated to only get the most important.

def fetch_value_in_table(input_table):
# Input table is like this : 
# [("val_number1", "c_shift", "h_shift1"), ("val_number2", "c_shift2", "h_shift2"), ("val_number3", "c_shift3", "h_shift3")]
# Global since output_table is used outside the function
global output_table

# Create the two necessary dictionaries
output_table = {}
dict_shift = {}

# Loop over a line that is actually a tuple like this :
# ("val_number1", "c_shift1", "h_shift1")
for line in input_table: 
    # OK
    val_number = line[0]

    # OK
    c_shift = line[1]
    dict_shift['c_shift'] = c_shift

    # OK
    #... truncated
    dict_shift['h_shift'] = h_shift


    output_table[val_number] = dict_shift
    #For first loop, should be :
    # {"val_number1": {"c_shift" = c_shift1, "h_shift" = "h_shift1" }}

    # Second loop : 
    # {"val_number1": {"c_shift" = c_shift1, "h_shift" = "h_shift1" }, "val_number2": {"c_shift" = c_shift2, "h_shift" = "h_shift2" }}
    # ...

return output_table

The expected result of output_table is:

{"val_number1": {"c_shift" = c_shift1, "h_shift" = "h_shift1" }, 
"val_number2": {"c_shift" = c_shift2, "h_shift" = "h_shift2" }, 
{"c_shift" = c_shift3, "h_shift" = "h_shift3"}}

But actually all the values are the last ones:

{"val_number1": {"c_shift" = c_shift3, "h_shift" = "h_shift3" }, 
"val_number2": {"c_shift" = c_shift3, "h_shift" = "h_shift3" }, 
{"c_shift" = c_shift3, "h_shift" = "h_shift3" }}

What do I miss to get the expected result ?

>Solution :

The dict_shift actually points to the same dictionary the whole time. You need to inicialize it (dict_shift = {}) inside the loop during each iteration.

def fetch_value_in_table(input_table):
global output_table

output_table = {}

for line in input_table: 

    val_number = line[0]
    dict_shift = {}

    c_shift = line[1]
    dict_shift['c_shift'] = c_shift
    dict_shift['h_shift'] = h_shift
    output_table[val_number] = dict_shift

return output_table