Python 3: How to understand this string

Question

I have a question, I am a beginner and I am reading the book "Introduction to Programming with Python" 3° Edition. And I came across this code below.

Program 4.3 - Income Tax Calculation

salario = float(input('Digite o salário para cálculo do imposto.: '))
base = salario
imposto = 0

if base > 3000:
    imposto = imposto + ((base - 3000) * 0.35)
    base = 3000
if base > 1000:
    imposto = imposto + ((base - 1000) * 0.20)

print(f'Salário: R${salario:6.2f} Imposto a pagar: R${imposto:6.2f}')

It is working but in this 'print' I did not understand "6.2f" being if I remove it will work the same way as in the example below.

Program 4.3 - Income Tax Calculation

salario = float(input('Digite o salário para cálculo do imposto.: '))
base = salario
imposto = 0

if base > 3000:
    imposto = imposto + ((base - 3000) * 0.35)
    base = 3000
if base > 1000:
    imposto = imposto + ((base - 1000) * 0.20)

print(f'Salário: R${salario} Imposto a pagar: R${imposto}')

Answer 1

Good afternoon Francisco, all good?

Francis, about the ':6.2f' is the following:

This corresponds to an output formatting in Python called Formatted Literal Strings or f-strings, as they are also known.

ABOUT THE ':6' : The number 6 after ':' helps you set the minimum size of this field by imposing a minimum number of characters, which basically serves to adjust the width of the field. If the field does not have at least 6 characters, Python adjusts it for you, and the width of the field will be at least 6 characters. If You test in your code and change this number by 10 you will see that the space between the 'R$' and the result gets bigger. Do tests, change 6 by 100 and you will see that the size only increases. The whole number after the ':', which in your script is 6, serves for this.

ABOUT THE '.2f' :
The . 2f is used to control the decimals, that is, after the comma, which in the case of Python is a '.' and not a comma, you will have two numbers. Just for example, if the result is R$ 2500.00, the . 2f worked to make sure that after the point you had two decimal places, as in the 00 example. Run tests, replace 2 by 10 and you’ll see that the number of decimals will increase.

About this type of formatting the Python documentation has some very interesting things, I’ll leave a link that can help.

https://docs.python.org/pt-br/3/tutorial/inputoutput.html#Tut-f-strings

I hope I helped. Good luck Francisco.

Answer 2

Documentation: https://docs.python.org/3/reference/lexical_analysis.html#f-strings

These are string formatting - the link above explains the options used with the 'format' method, which work the same way for f-strings. After the expression, inside a pair of keys in an "f-string", you can use the "!" , ":" or "=" (Python 3.8) to specify how the result of the expression will be shown. In the case of ":6.2f" it means: "format the number as a decimal with 6 digits, being 2 after the decimal point". By default, the output is aligned to the right, filling the remaining digits with spaces".