Choosing a name¶

Variables store a value in memory to re-use a result later without redoing the calculation. It also simplifies the understanding of the code.

In Python a variable is a word with as a letter all the alphanumeric characters as well as the _ but it can not start with a number.

   * yes: PiaNo piano P_ i _a_ n _O * no: 666 666piano By convention we use _ for a variable with several words: my _age, average_ notes

Assignment¶

Assigning a value to a variable is done with the = sign

In [1]:
age = 42
print(age)

42

Comparison¶

Note that the comparison uses the == sign (see Course on Tests)

Modification¶

I can modify my variable:

In [2]:
age = 45
print(age)
age = age + 1
print(age)

45
46

The assignment is not an equality in the mathematical sense otherwise age = age + 1 would not make much sense. This line indicates that the variable age will receive the value of the variable plus one.

The incrementation of a variable is so usual that we defined the operator + = for that:

In [3]:
age += 1
print(age)
age += 3
print(age)

47
50
In [4]:
print(age == 42)
print(age == 41)

False
False

There are also the * = / = and - = operators

Exercise¶

Convert the temperature 100 degrees Fahrenheit to Celcius knowing that celcius = 5/9 * (fahrenheit - 32) and display the result.

In [5]:
ma_temp_f = 100

Of course operators / and * have priority over + and -. At equal level, the operations are from left to right.

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