neval 0.0.5

Execute raw Python code in an isolated namespace

neval — Namespaced code evaluator

This package provides an alternative scoping mechanism to the standard exec and eval functions for running raw Python code. The goal is to overcome the following behaviour of exec, as describe in the docs:

If exec gets two separate objects as globals and locals, the code will be executed as if it were embedded in a class definition.

For instance, when you want to use locals as a staging scope and globals as an accessible backdrop, the executed code can quickly result in unexpected behaviour. For example:

# ✓ [1]
exec("a=[1]; print([i for i in a])", {}, {})

# ✗ NameError: name 'a' is not defined
exec("a=[1]; print([i for i in a if a])", {}, {})

# ✓ os
exec("import os; print(os.__name__)", {}, {})
 
# ✗ NameError: name 'os' is not defined
exec("import os; (lambda: print(os.__name__))()", {}, {})

Runcode's alternative evaluation

The main difference is that neval has two arguments called namespace for reflecting scope changes (almost like locals) and namespace_readonly to additionally draw from (almost like globals). The main deviations are:

• namespace is a dict or a __dict__ attributed object whose keys are read and written to reflect scope changes
• namespace_readonly is a dict or a __dict__ attributed object whose keys are only read, but not written
• if the last statement in the code is an expression, the executed value of the expression is returned
• if an error occurs, a temp file is generated in order for C interpreter to provide a more informative error message (after Python teardown)
• for Python >= 3.11 the traceback includes a printout of the code using the new add_note feature, similarly to ipython

  File "/temp/neval-057d58343544b6d102cac201bdc11527a0224e87", line 3, in <module>
    c = 4/0
        ~^~
ZeroDivisionError: division by zero
Error in neval-057d58343544b6d102cac201bdc11527a0224e87:
      1 a = 1
----> 3 b = 4/0
      4 c = 5

Examples

from neval import neval

neval("a = 1; b = 2; c = 3; d = 4; a + b + c + d")
# ✓ 10

neval("a = 1; b = 2; c = 3; d = 4; a + b + c + d", ns:={})
# ✓ 10

ns
# ✓ {'a': 1, 'b': 2, 'c': 3, 'd': 4}

import numpy as np
from types import SimpleNamespace

neval("a = argmax(array([1,2,3,4,3,2,1])**2)", ns:=SimpleNamespace(), np)

ns.a
# ✓ 3

a,b,c = (1,2,3)

neval("d = a + b*2 + c*3", ns:=SimpleNamespace(), globals())

ns.d
# ✓ 14

d
# ✗ NameError: name 'd' is not defined

neval("d = a + b*2 + c*3", globals())

d
# ✓ 14

params = SimpleNamespace(a=1, b=2, c=3)

neval("d = a + b*2 + c*3", params)

params
# ✓ namespace(a=1, b=2, c=3, d=14)

neval("""\
a = 1 + 2
this is incorrect
b = a + 3
""")
# ✗ NameError: name 'this' is not defined
#   Error in neval-8efcb70d4b63817f9fd92f3b61eb5a7c0c45cfe9:
#         1 a = 1 + 2
#   ----> 2 this is incorrect
#         3 b = a + 3