Question

Variables in Python are defined and typed for you when you set a value to them.

my_variable = 2
print(my_variable)
type(my_variable)

2

int

This makes variable definition easy for the programmer. As usual, though, great power comes with great responsibility. For example:

my_varible = my_variable+1
print (my_variable)

2

“If you leave out word, spell-check will not put the word in you” – Taylor Mali, The the impotence of proofreading

If you accidentally mistype a variable name, Python will not catch it for you. This can lead to bugs that can be hard to track - so beware.

Types and Typecasting

The usual typecasting is available in Python, so it is easy to convert strings to ints or floats, floats to ints, etc. The syntax is slightly different than C:

a = "1"
b = 5
print(a+b)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

<ipython-input-3-6463279979e9> in <module>()
      1 a = "1"
      2 b = 5
----> 3 print(a+b)


TypeError: cannot concatenate 'str' and 'int' objects

a = "1"
b = 5
print(int(a)+b)

Note that the typing is dynamic. I.e. a variable that was initally say an integer can become another type (float, string, etc.) via reassignment.

a = "1"
type(a)
print(type(a))

a = 1.0
print(type(a))

Python has some other special data types such as lists, tuples and dictionaries that we will address later.