Difficulty assigning variables in python-CodePudding

I'm trying to write a very basic Python program to calculate the number of minutes per week.

I've created an Hr_Per_Day variable, but when I update this variable, min_per_day, which should update, doesn't. Why not?

Here's the code:

Hr_Per_Day = 24
min_per_day = Hr_Per_Day * 60
min_per_day
**OUTPUT: 1440**
Hr_Per_Day = 26
min_per_day
**OUTPUT: 1440**

Why doesn't min_per_day update after I change Hr_Per_Day to 24? Any help would be appreciated!

I expected min_per_day to update after changing Hr_Per_Day.

CodePudding user response：

min_per_day = Hr_Per_Day * 60

It seems like you expect this assignment to act like an ongoing formula, and if Hr_Per_Day ever changes, then min_per_day will also change.

Python doesn't work that way.

That assignment is a one-time calculation, using the value of Hr_Per_Day at that moment. If that value changes later, it will have no effect on min_per_day.

CodePudding user response：

Its important to understand two things:

Python statements are run one by one and are always completed before the next statement is run.
Variables hold values - each variable can hold 1 value that cannot be changed - the variable can be assigned a new value, but the value itself never changes.

So in your case, you calculate the value of min_per_day by reading the value of Hr_Per_day and doing a mathematical operation on it, then the result is stored in the variable min_per_day.

After that, if you assign a new value to the variable Hr_Per_Day, it cannot change the result of the previous statement. If you want to tell Python to recalculate the value for min_per_day based on the new value of Hr_Per_Day, you have to run the calculation statement again - something like this:

Hr_Per_Day = 24
min_per_day = Hr_Per_Day * 60
print(min_per_day)
# Output: 1440

Hr_Per_Day = 26
min_per_day = Hr_Per_Day * 60
print(min_per_day)
# Output: 1560