Learn Python: Python Variables
As with all other languages, Python has variables which can be defined to hold data. As we learn about python variables, it is important to remember a few fundamental things about Python:
- It is dynamically typed, so variables can change type - and Python infers the type of variables from their content.
Let’s start learning about how we define variables. First, make a file called
variables.py, and let’s start experimenting.
Standard variable definition
x with a value
Hello World (string) - then we just do the following to create the variable, and then print it:
x = "Hello World" print(x)
We can test this out in our
variables.py file by saving this, and running
python variables.py from terminal, when we are in the directory where
variables.py is stored. If, for whatever reason, the
python command cannot be found, you can learn how to resolve that here.
As in other languages, we have multiple types. Here are a few examples:
w = "Hello World" # String x = 1 # Int y = 2.5 # Float z = True # Boolean print(w, x, y, z)
One difference from some other languages, is when defining a boolean, we use capital letters - so you have to write
True. We can find out the types of any variable using the
w = "Hello World" # String x = 1 # Int y = 2.5 # Float z = True # Boolean # Will return <class 'int'> print(type(x))
Defining multiple variables at once
We can also define multiple variables at once in Python using the comma notation. So, if we wanted to define
z on one line, we could do it like this:
w, x, y, z = ("Hello World", 1, 2.5, True); print(w, x, y, z);
Just like other languages, we can concatenate variables if needed. We create a string concatenation like so:
location = "World" print("Hello " + location)
Note: as previously mentioned, we can only concatenate strings of the same type. So if we try to concatenate an
int instead, we’ll get an error:
day = 6 # Throws an error: TypeError: can only concatenate str (not "int") to str print("It is day " + day)
To resolve this, we can use type casting.
So, as mentioned, we can’t concatenate variables of differing types. If we want to force an
int to be
string so we can concatenate it with another
string, we need to use casting. To do that, we use functions like
str(), which will force it’s content to cast to a string.
day = 6 # Throws an error: TypeError: can only concatenate str (not "int") to str print("It is day " + str(day))
Other types of casting
As well as
str(), there are 2 other casting functions in Python:
int()- creates an integer from a string, integer, or float.
float()- creates a float from a string, integer or float.
These can easily be used in your code just like we used
str() above. Here are some examples:
x = 5 # Int y = 2.5 # Float z = "Hi" # String a = "5" # String xFloat = float(x) yInt = int(y) aInt = int(a) # Will return 5.0 2 5 print(xFloat, yInt, aInt)
Note: if you try to convert
z above to an
float, it will throw an error - since the text
"Hi" cannot be interpreted as a float or integer. The error we’d get looks like this:
ValueError: invalid literal for int() with base 10: 'Hi'
Python variables work in the same way as most other languages, but there are some differences if you are coming from a different background. In this guide, we’ve covered the fundamentals. If you want to stay in the loop, follow me on twitter for more python tutorials.