1 - Declaration of variables in python
A variable is
a kind of virtual box in which we can put one (or more) data (s). The idea
is to temporarily store data to work with. For your machine a variable is an
address that indicates the location of the RAM where the information we have
linked is stored.
Python is a dynamically typed language, which means you do not have to declare the type of the variable. So to declare a variable in python, we directly introduce its name followed by its value:
Python is a dynamically typed language, which means you do not have to declare the type of the variable. So to declare a variable in python, we directly introduce its name followed by its value:
Example
>>> x = 5 >>> # here we introduce a variable whose value is 5 >>> x 5
2 - Variable names and reserved words
Under Python,
variable names must follow a few simple rules:
-
A variable name is a sequence of letters a..z, A..Z and digits 0 .. 9, which must always begin with a letter.
-
Only ordinary letters are allowed. Accented letters, cedillas, spaces, special characters such as $, #, @, etc. are prohibited except for the _ character.
-
The case is significant (uppercase and lowercase characters are distinguished).
Warning ! : Phone, phone,
PHONE are therefore different variables. Be careful !
In addition to these rules, it must be added that you can not use as variable names the 29 "reserved words" below (they are used by the Python language itself):
In addition to these rules, it must be added that you can not use as variable names the 29 "reserved words" below (they are used by the Python language itself):
and, assert, break, class,
continue, def, del, elif, else, except, exec, finally, for, from,
global, if, import, in, is, lambda, not, or, pass, print, raise,
return, try, while, yield
3 - Types of variables
In python a
variable is dynamically typed, ie by introducing a variable followed by its
value, Python detects its type:
Example
>>> h = "Hello" >>> h Hello In this example Python detects that this is a string whose value is "Hello"
-
Integer : as its name indicates an integer is a digit without decimals.
-
Floats or number with commas: example: 1.5
-
Strings or string of characters : to simplify everything that is not a number.
There are many
others but, to simplify the task we will not mention all types here.
Note
To know the
type of a variable, you can use the "type
()" function
Example
>>> x=5 >>> # Here we define a variable of Integer type >>> type(x) class int="" >>> a="android phone" >>> # Here we define a varible of String type >>> type(a) class str="" >>> ram=4.5 >>> # Here we define a varible of float type >>> type(ram) class float=""
3 - Operations on the variables
Operators are
symbols that manipulate variables, that is perform operations, evaluate
them, ... There are several types of operators : calculation
operators, assignment operators, comparison operators, logical operators,
...
3 - 1 Calculation operators
Calculation
operators allow to mathematically modify the value of a variable :
-
"+" addition operator Adds two values
-
"-" subtraction operator Subtracts two values
-
"*" multiplication operator Multiplies two values
-
"/ " division operator Divides two values
-
"=" assignment operator Assigns a value to a variable : x = 3 Put the value 3 in the variable x.
3 - 2 Assignment Operators
These
operators simplify operations such as adding a value to a variable and
storing the result in the variable. For example: x = x + 2
With the assignment operators it is possible to write this operation in the following form: x + = 2.
That is, if x = 3 it becomes after the operation 5.
With the assignment operators it is possible to write this operation in the following form: x + = 2.
That is, if x = 3 it becomes after the operation 5.
3 - 3 Concatenation of variables
The
concatenation of two strings variables is the operation of putting one of
the strings followed by the other and storing the result in another variable
Example
>>> d="Desk" >>> t="top" >>> dt=d+t >>> # Here dt is the concatenation of "Desk" and "top" and take as value "Desktop" >>> dt 'Desktop'
Note : You can note concatenate a string variable with a numerical variable. But you can do it after transformation from the numeric type to the string type with the str() method.
Example
>>> ram=5.6 >>> print("The ram value is equal to : " + str(ram)) The ram value is equal to : 5.6
Younes Derfoufi