Prothon Tutorial

 Prothon Home Previous Page Tutorial Outline Next Page

2.0 Introduction to Prothon

2.1 Comments

Any line starting with the hash symbol, aka pound-sign ( # ), is a comment line and is ignored by the interpreter. If the hash symbol appears in the middle of the line, then the rest of the line is ignored.

>>> # print "Hello"
>>> print "hello" #, "world"
hello
>>>

You can also use C-style inline comments /* ... */ in the middle of a line of code or to block out large sections of code easily in a file:

>>> print "hello" /* "there" */ , "world"
hello world
>>>

2.2 Indentation

Almost all languages have code blocks. These are multiple lines of code that are logically grouped together to be executed as one unit of code. In the C language for example, a code block is surrounded by braces "{" and "}"

/* This is C code, NOT Prothon code*/
if (x) 
    {
    do_something(); 
    do_more(); 
    }

In Prothon (and Python) the braces aren't needed. The indentation that programmers usually use to help show the block structure anyway, is itself the indicator of the blocks.

The indentation rule is that when a new block is needed, a line will end in a colon. Then the next line, which is the first line of the block, is indented. Each line of that block then must be indented the same amount to show it belongs to that block.

Blocks can be nested by having nested indentation, but lines further down that go back to the left again must line up with a line above to show which block it belongs to.

# Prothon code
if x:
    do_something()
    do_more()
    if y:
        do_even_more()    # new nested block
    do_more()             # back to same block
Important: Mixing Spaces and Tabs: You may use either spaces or tabs to indent your blocks, but in any one group of nested blocks, you may not intermix spaces and tabs. You will get an error if you do. The reason for this rule is that mixed spaces and tabs would cause the lines to not line up on editors with tab widths set differently.

2.3 Line Continuations

When a Prothon line is too long to fit in your text editor comfortably, you can spread it across two or more lines by continuing a line of code on the next line. Some of these ways don't work in the console so I'll just show you examples here.

There are three ways to indicate a line continuation. The first is to end a line with the backslash character ( \ ), making sure that it is the very last character. This even works inside a string:

x = "Hello \
     World"

Another way to continue a line is to end a line while a left parentheses, bracket, or brace: (, [, or {, still does not have it's matching right partner. The interpreter knows the line must be continued until all such characters partner's are matched up:

x = 3 * (5 +
         4 + 6)

Finally, the last way to continue a line is to indent a line when the previous line does not end in a colon. Note that you must still follow the indent rules, so if you are using tabs for indents you must tab in at least once before using spaces for alignment:

x = factor(a,b)+
    factor(c,d)

 

 Prothon Home Previous Page Tutorial Outline Next Page