This package is dedicated to parse and work with various languages, in particular Python itself and ABCD. These are mainly utilities for internal use in SNAKES, however, they may be of general interest independently of SNAKES.

Module ast

The module ast exported by snakes.lang is similar to Python's standard ast module (starting from version 2.6) but is available and uniform on every implementation of Python supported by SNAKES: CPython from 2.5, Jython and PyPy. (In general, these modules are available in these implementation - except CPython 2.5 - but with slight differences, so using snakes.lang.ast can be seen as a portable implementation.)

Notice that this module is not available for direct import but is exposed as a member of snakes.lang. Moreover, when snakes.lang is loaded, this module ast is also loaded as snkast in sys.modules, this allows to have both versions from Python and SNAKES simultaneously.

>>> import snakes.lang.ast as ast
ImportError ...
 ...
ImportError: No module named ast
>>> from snakes.lang import ast
>>> import snkast

Function getvars

def getvars (expr) :

Return the set of variables (or names in general) involved in a Python expression.

>>> list(sorted(getvars('x+y<z')))
['x', 'y', 'z']
>>> list(sorted(getvars('x+y<z+f(3,t)')))
['f', 't', 'x', 'y', 'z']

Call API

• str expr: a Python expression
• return set: the set of variable names as strings

Function rename

def rename (expr, map={}, **ren) :

Rename variables (ie, names) in a Python expression

>>> rename('x+y<z', x='t')
'((t + y) < z)'
>>> rename('x+y<z+f(3,t)', f='g', t='z', z='t')
'((x + y) < (t + g(3, z)))'
>>> rename('[x+y for x in range(3)]', x='z')
'[(x + y) for x in range(3)]'
>>> rename('[x+y for x in range(3)]', y='z')
'[(x + z) for x in range(3)]'

Call API

• str expr: a Python expression
• dict map: a mapping from old to new names (str to str)
• str ren: additional mapping of old to new names
• return str: the new expression

Function bind

def bind (expr, map={}, **ren) :

Replace variables (ie, names) in an expression with other expressions. The replacements should be provided as ast nodes, and so could be arbitrary expression.

>>> bind('x+y<z', x=ast.Num(n=2))
'((2 + y) < z)'
>>> bind('x+y<z', y=ast.Num(n=2))
'((x + 2) < z)'
>>> bind('[x+y for x in range(3)]', x=ast.Num(n=2))
'[(x + y) for x in range(3)]'
>>> bind('[x+y for x in range(3)]', y=ast.Num(n=2))
'[(x + 2) for x in range(3)]'

Call API

• str expr: a Python expression
• dict map: a mapping from old to new names (str to ast.AST)
• ast.AST ren: additional mapping of old to new names
• return str: the new expression