String Format .format to variable

Question

I'm trying to create a function that allows me to pass in a string into an age variable using a while loop. This is the simplified version of the code using the .format string. The following code works as expected.

num = 1
while num<7:
    age = 'My age is {}'.format(num)
    print(age)
    num+=2

The output is as shown below:

My age is 1
My age is 3
My age is 5

However, when I attempt to capture the string 'My age is {}' in the age variable using the while loop it doesn't work. Here is the code.

num = 1
age = 'My age is {}'
while num<7:
    age = age.format(num)
    print(age)
    num+=2

I get the following output.

My age is 1
My age is 1
My age is 1

Any idea the reason the num does not increment in the while loop in the second example? What's the solution?

Answer 1

You're overwriting the age string so there's nothing left to format in the second iteration. You could use two strings - one with the template to format in to, and one with the formatted result:

num = 1
template = 'My age is {}'
while num<7:
    age = template.format(num)
    print(age)
    num+=2

Answer 2

The first time through the loop, you've replaced the {} in the string with a number. From that point forward, format doesn't have anything to do since the string doesn't have any formatting markers in it.