1.2.1. First steps

Start the Ipython shell (an enhanced interactive Python shell):

• by typing “ipython” from a Linux/Mac terminal, or from the Windows cmd shell,

• or by starting the program from a menu, e.g. the Anaconda Navigator, the Python(x,y) menu if you have installed one of these scientific-Python suites.

If you don’t have Ipython installed on your c...

If you don’t have Ipython installed on your computer, other Python shells are available, such as the plain Python shell started by typing “python” in a terminal, or the Idle interpreter. However, we advise to use the Ipython shell because of its enhanced features, especially for interactive scientific computing.

Once you have started the interpreter, type

>>> print("Hello, world!")
Hello, world!

The message “Hello, world!” is then displayed...

The message “Hello, world!” is then displayed. You just executed your first Python instruction, congratulations!

To get yourself started, type the following stack of instructions

>>> a = 3
>>> b = 2*a
>>> type(b)
<class 'int'>
>>> print(b)
6
>>> a*b
18
>>> b = 'hello'
>>> type(b)
<class 'str'>
>>> b + b
'hellohello'
>>> 2*b
'hellohello'

Two variables a and b have been defined above...

Two variables a and b have been defined above. Note that one does not declare the type of a variable before assigning its value. In C, conversely, one should write:

int a = 3;

In addition, the type of a variable may change, in the sense that at one point in time it can be equal to a value of a certain type, and a second point in time, it can be equal to a value of a different type. b was first equal to an integer, but it became equal to a string when it was assigned the value ‘hello’. Operations on integers (b=2*a) are coded natively in Python, and so are some operations on strings such as additions and multiplications, which amount respectively to concatenation and repetition.