Member Avatar for KrazyKitsune

Is it possible for the user to input a Python snippet and run it? Like this:

x = raw_input("Python snippet: ") #And then run the script typed in here

Also, we know how errors happen all the time. Is it possible to make it so that when errors happen because there was something invalid inputted into a raw_input (or otherwise any inputting function), a print function pops up and defines the error?

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Yes — user-entered Python can be executed, but with important caveats. As noted, eval() evaluates a single expression and returns its value, while exec() runs statements (definitions, loops, etc.). Note the Python version difference: Python 2’s raw_input() returns a string; Python 3’s input() behaves the same as Python 2’s raw_input() (see the built-ins for details: https://docs.python.org/3/library/functions.html#eval). Execution of arbitrary text is powerful and potentially dangerous.

For safe parsing of simple literals (numbers, strings, tuples, lists, dicts, booleans, None) prefer ast.literal_eval() instead of eval():

import ast

s = input("literal: ")
try:
    value = ast.literal_eval(s)
    print("Parsed:", value)
except (ValueError, SyntaxError) as e:
    print("Invalid literal:", e)

ast.literal_eval is limited but far safer for untrusted input (docs: https://docs.python.org/3/library/ast.html#ast.literal_eval). For full code execution the error-reporting advice from still applies: wrap calls in try/except and present either the exception message or a full traceback when debugging. Example pattern:

import traceback

try:
    exec(user_code, {"__builtins__": {}}, {})
except Exception:
    traceback.print_exc()

Do not rely on naive builtin removal for security — sandboxing Python correctly is hard. For running truly untrusted snippets, run them in a separate process or container with strict resource/time limits, or use a well-maintained sandboxing library. For user-facing error messages, catch specific exceptions where possible and convert them to clear, short messages rather than dumping raw traces (use full tracebacks only for logging or developer debugging). For exception syntax and handling patterns, see the Python tutorial on exceptions: https://docs.python.org/3/tutorial/errors.html#handling-exceptions.

Summary: use ast.literal_eval for simple inputs, exec/eval only when necessary and never on untrusted text without isolation, and use try/except (and traceback) to capture and display errors as and suggested.

Recommended Answers

All 4 Replies

Member Avatar for jcao219

See the exec and eval functions.

Member Avatar for KrazyKitsune

What about the error one?

Member Avatar for TrustyTony

See try...except.,else...finaly for error handling.

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