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I'm sorry for the rudimentary question about Python's For statement,
The following formula does not show why the compounding of the principals (Savings) is calculated.

``````savings = 100
for i in range (15):
savings + = savings * 0.05
print (savings)``````

This result is about 207.9 (15-year compound interest calculation with a principal of 100 and an interest rate of 5%).
If savings + = savings * 0.05, then 100 + 100 * 0.05 would be 105, and that would be repeated 15 times.

saing changes in the loop.
Try executing the print statement.

``````savings = 100
for i in range (15):
print (savings)
savings + = savings * 0.05
print (savings)``````

Execution example

15% interest rate of 15% Since the annual compounding calculation,`savings + = savings * 0.05`can be rewritten as`savings * = 1.05`. You will see whether savings * 0.05is fine.

As Katoy mentioned,`savings`is avariablethat changes with each loop.

``````savings = 100
for i in range (15):
savings * = 1.05
print (savings)
print (savings)``````

savings + = savings * 0.05 is

Savings = savings + savings * 0.05

If you transform the formula
You can also write savings = savings * 1.05

If this is the case
It is the definition of compound interest calculation itself.

``````savings = 100
for i in range (15):
print (savings) # try to write output
savings = savings * 1.05
print (savings)``````

The results are printed below.
100
105.0
110.25
115.7625
121.55062500000001
127.62815625000002
134.00956406250003
140.71004226562505
147.74554437890632
155.13282159785163
162.8894626777442
171.03393581163144
179.58563260221302
188.56491423232367
197.99315994393987
207.89281794113688