Python 2.7 : Numerical variable

It is impossible to write a program without using a variable. This term refers to the fact of assigning a name or identifier to information: by naming them, one can manipulate this information much more easily. The other advantage is to be able to write programs that are valid for values that vary: you can change the value of variables, the program will always run in the same way and do the same types of calculations whatever the values manipulated. The variables play a role similar to the unknowns in a mathematical equation. The computer cannot add more than two numbers, but this is sufficient to calculate the sum of the first n integers. To do this, it is necessary to create an intermediate variable that we will call sum, for example, in order to keep the result of the intermediate sums. To define the name of a variable in Python, you can use letters, lower or upper case, and numbers. It is also possible to use the underscore character: _ . However, the variable name must not start with a number. So variable_1 is accepted by Python.