One of the beneﬁts of working with an interpreted language is that you can test bits of code in interactive mode before you put them in a script. But there are differences between interactive mode and script mode that can be confusing.
For example, if you are using Python as a calculator, you might type
>>> miles = 26.2>>> miles * 1.6142.182
The ﬁrst line assigns a value to miles, but it has no visible effect. The second line is an expression, so the interpreter evaluates it and displays the result. So we learn that a marathon is about 42 kilometers.
But if you type the same code into a script and run it, you get no output at all. In script mode an expression, all by itself, has no visible effect. Python actually evaluates the expression, but it doesn’t display the value unless you tell it to:
miles = 26.2print miles * 1.61
This behavior can be confusing at ﬁrst.
A script usually contains a sequence of statements. If there is more than one statement, the results appear one at a time as the statements execute.
For example, the script
print 1x = 2print x
produces the output
The assignment statement produces no output.
Exercise 2.1.Type the following statements in the Python interpreter to see what they do:
5 x=5 x+1
Now put the same statements into a script and run it. What is the output? Modify the script by transforming each expression into a print statement and then run it again.