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. in the Python(x,y) or EPD menu if you have installed one of these scientific-Python suites.
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. 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) <type 'int'> >>> print(b) 6 >>> a*b 18 >>> b = 'hello' >>> type(b) <type 'str'> >>> b + b 'hellohello' >>> 2*b 'hellohello'
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
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.