sourcer 0.1.2

simple parsing library

Simple parsing library for Python.

There’s not much documentation yet, and the performance is probably pretty bad, but if you want to give it a try, go for it!

Feel free to send me your feedback at [e-mail]. Or use the github issue tracker.

Installation

To install sourcer:

pip install sourcer

If pip is not installed, use easy_install:

easy_install sourcer

Or download the source from github and install with:

python setup.py install

Example: Hello, World!

Let’s parse the string “Hello, World!” (just to make sure the basics work):

from sourcer import *

# Let's parse strings like "Hello, foo!", and just keep the "foo" part:
greeting = 'Hello' >> Opt(',') >> ' ' >> Pattern(r'\w+') << '!'

# Let's try it on the string "Hello, World!"
person1 = parse(greeting, 'Hello, World!')
assert person1 == 'World'

# Now let's try omitting the comma, since we made it optional (with "Opt"):
person2 = parse(greeting, 'Hello Chief!')
assert person2 == 'Chief'

Example: Parsing Arithmetic Expressions

Here’s a quick example showing how to use operator precedence parsing:

from sourcer import *

Int = Pattern(r'\d+') * int
Parens = '(' >> ForwardRef(lambda: Expr) << ')'
Expr = OperatorPrecedence(
    Int | Parens,
    InfixRight('^'),
    Prefix('+', '-'),
    Postfix('%'),
    InfixLeft('*', '/'),
    InfixLeft('+', '-'),
)
ans = parse(Expr, '1+2^3/4')
assert ans == Operation(1, '+', Operation(Operation(2, '^', 3), '/', 4))

Some notes about this example:

• The Pattern term means “Compile the argument as a regular expression and return the matching string.”

• The * operator means take the parse-result from the left operand and then apply the function on the right. In this case, the transform function is simply int.

• So in our example, the Int rule matches any string of digit characters and produces the corresponding int value.

• The >> operator means “Discard the result from the left operand. Just return the result from the right operand.”

• The << operator similarly means “Just return the result from the result from the left operand and discard the result from the right operand.”

• So the Parens rule in our example parses an expression in parentheses and simply discards the parentheses.

• The ForwardRef term is necessary because the Parens rule wants to refer to the Expr rule, but it hasn’t been defined by that point.

• The OperatorPrecedence rule constructs the operator precedence table. It parses operations and returns Operation objects.

More Examples

Parsing Excel formula and some corresponding test cases.