Simple Python module to help with code generation
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pics README Oct 4, 2017 spelling of rectangular in Oct 7, 2017 Do not omit empty lines in the middle of a tile May 31, 2018


Tiles is a simple Python module meant to help with code generation. It provides a way to work with rectangular areas of text as atomic units. This is particularly important if proper indentation of generated code is desired.

Tile is a standard Python string. However, one should keep in mind that it's just the rectangular area of text that counts. All the surrounding whitespace has no significance.

The module provides a single function that can be used to combine smaller tiles to create larger tiles:

from tiles import tile

colors = """

shapes = """

output = tile("""
              Colors: @{colors}     Shapes: @{shapes}

              That's all, folks!

print output

The output looks like this (expanded tiles marked in red):

Worked example

Imagine that we want to generate code that prints out some greetings.

def greet(name):
    return "print 'Hello, " + name + "!'\nprint 'Welcome!'" 

Although there is no particular need for manipulating rectangular areas of text in this case tiling can be employed to make the code more readable.

def greet(name):
    return tile("""
                print 'Hello, @{name}!'
                print 'Welcome!'

Given that whitespace surrounding the tile is ignored anyway we can neatly align the generated code with the generator code instead of writing an abomination like this:

def greet(name):
    return tile("""print 'Hello, @{name}!'
print 'Welcome!'""")

Another consequence of using tiles is that the greeting function can be used in different contexts and the indentation will allways fit.

code = tile("""
            import sys

            if 'also-greet-bob' in sys.argv:

print code

Here's the output. Note how the greeting code is properly aligned in both cases, thus forming a valid Python program.

import sys

print 'Hello, Alice!'
print 'Welcome!'
if 'also-greet-bob' in sys.argv:
    print 'Hello, Bob!'
    print 'Welcome!

Another worked example

Tiling can be also used to generate code with clean vertical alignment. Consider the case where we have a lists or argument names and types and we want to generate a nicely formatted C function declaration.

args = ["foo", "bar", "baz"]
types = ["int", "char*", "struct quux"]

print tile(r'void frobnicate('
           r'@{"\n".join(types)} '
           r'@{",\n" * (len(args) - 1) + ");"}'

The tile with argument names is put next to the tile with argument types. This is done on tile, not line, level which means that all the argument names stay aligned with each other.

void frobnicate(int         foo, 
                char*       bar,
                struct quux baz);

Tiling algorithm

For reference, this is how the tiling algorithm works.

It parses the supplied string line by line. Each line consists of literal text mixed with @{} expressions. Each piece of literal text is kept as is. Each @{} expression is evaluated and replaced by the resulting tile. Both the literal text and the tiles are aligned to the top of the line.

Thus, a line like this:

Colors: @{colors}     Shapes: @{shapes}

That's all, folks!

Is rendered like this. Tiles are shown in red frames. Literal text is in blue frames. Black lines mark boundaries between individual lines.

Note 1: Output of tile() function itself is not stripped off the surrounding whitespace. This allows for generating programs that start or end with empty lines. If you want to remove the whitespace you can do so like this: tile("@{code}")

Note 2: If you need sequence @{ to appear in the output (and not be treated like an embedded expression) it can be done like this: @{'@'}{

Note 3: The trailing whitespace that is required to keep the rectangular shape of a tile doesn't get into the output. This makes the algorithm friendy to different tools that complain about whitespace at the end of a line.