Literal

Literal is a project to create a way to generate Python code with Python code. Instead of having string literals of Python code, you use literal.py objects that remembers the operations done to them, and the history of operations is the resulting Python program.

This is just an experiment that I wanted to play with; It's usefulness is not proven, and more than likely this will be thrown away as a failed experiment. So use with care and caution.

Quick overview

import literal

@literal.py
def unpack_octet(x, payload, offset, unpack_from):
 x < < = unpack_from('B', payload, offset)
 offset += 1

print(unpack_octet())

Gives:

x = unpack_from('B', payload, offset)
offset += 1

Or another example used to create argument unpackers for the AMQP protocol:

def unpack(method):

 @literal.py
 def body(p, payload, offset, unpack_from, argtuple, ssize):
 fields = method.fields
 names = p.tuple(*self.field_names)

 for i, fset in enumerate(fields):
 if len(fset) == 1:
 for field in fset:
 name = p.var(field.name)
 if field.format == '*':
 # This is a string payload,
 # don't have to unpack
 name < < = payload[offset:offset + ssize]
 offset += ssize
 else:
 # A single field to unpack
 name < < = unpack_from(struct_format(field.format),
 payload, offset)[0]
 offset += field.size
 else:
 # A list of field to unpack
 these = p.tuple(*fset.names)
 these < < = unpack_from(struct_format(fset.format),
 payload, offset)
 offset += sum(f.size for f in fset)
 return names

 return body().as_fun(lambda payload, offset: 1,
 method.name)

Would generate the following code for the AMQP method basic_deliver:

def deliver(payload, offset):
 ssize = unpack_from('B', payload, offset)[0]
 offset += 1
 consumer_tag = payload[offset:offset + ssize]
 offset += ssize
 delivery_tag, redelivered, ssize = unpack_from('QBB', payload, offset)
 offset += 10
 exchange = payload[offset:offset + ssize]
 offset += ssize
 ssize = unpack_from('B', payload, offset)[0]
 offset += 1
 routing_key = payload[offset:offset + ssize]
 offset += ssize
 return (consumer_tag, delivery_tag, redelivered,
 exchange, routing_key)

More documentation to come.

Installation

You can install literal either via the Python Package Index (PyPI) or from source.

To install using pip:

pip install literal

To install using easy_install:

 easy_install literal

If you have downloaded a source tarball you can install it by doing the following:

 python setup.py build
# python setup.py install # as root

Bug tracker

If you have any suggestions, bug reports or annoyances please report them to our issue tracker at http://github.com/ask/literal.py/issues/

Contributing

Development of literal.py happens at Github: http://github.com/ask/literal.py

You are highly encouraged to participate in the development. If you don't like Github (for some reason) you're welcome to send regular patches.

Requirements:

• Python