Now, let us move from a simple statement to a command for Jack:
Throw the ball to Jane!
Here, of course,
one is telling Jack to do something, 'throw', to an object, 'the
ball', with a desired recipient, 'Jane'.
In programming, the
computer is always the one that does things. What is to be done
is, obviously, what you tell Jack, or the computer, to do. In most
instances, however, if you do not tell the computer
what you
want it to act upon, it will not know what you mean. In this example,
it will go looking for more information and find 'the ball'. However,
the computer, being a bit clueless without your help, will still not
know what to do. 'Throwing' carries a sense of direction with it, and
the computer will want to know where you want the ball thrown. If the
command was 'hold', Jack (and the computer) would know to simply sit
still and hold the ball. But throwing requires direction and so one
must give Jack (and the computer) an endpoint: Jane. Just like in
human language, if we leave out any part of the sentence, confusion
fills the gap.
These pieces of more information are what computer programmers
call "arguments". Commands can require no arguments or
several. Sometimes a command knows to assume information, a default
setting, if other information is not given. Other times, however, the
Python interpreter will look for more information, not find any, and
quit without finishing the program (aka, "throw an error").
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