safefunc

Important

You may want to use the newer library fnsafe.

Make sudden erros not stop your program

Installation

pip install safefunc

from safefunc import makesafe

Basic Example

@makesafe()
def divide(a, b):
    return a / b

print("Let's calculate!")
result = divide(1, 0)
print(f"{result = }")

Output:

Let's calculate!
Ignoring exception in divide
Traceback (most recent call last):
  File "<string>", line 40, in safe
  File "<string>", line 75, in divide
ZeroDivisionError: division by zero
result = None

As you can see, the exception gets printed but the program continues.

More Examples

Let's try the same thing with divide(1, 1):

Output:

Let's calculate!
result = 1

Now everything worked fine.

Some functions may return None. If an error happens, it would also return None. Luckily we can differate between success and failure with the return_entire_result paramter:

@makesafe(return_entire_result = True)
def divide(a, b):
    return a / b

print("Let's calculate!")
result = divide(1, 0)
if result: # or result.success
    print(result()) # or result.result

In this case our function returns a Result object which allows us to check wether the function succeeded or not. The result attribute (which also can be accessed by calling the object) returns depending on the success, the function return value or the exception.

Let's expect, we call divide("1", 1). Because the first argument is not supported for division, it would raise an error. If we only want to ignore ZeroDivisionErrors, we can make use of the ignore parameter. You can interpret this as a whitelist:

@makesafe(return_entire_result = True, ignore = [ZeroDivisionError])
def divide(a, b):
    return a / b

print("Let's calculate!")
result = divide("1", 1)
if result:
    print(result())

This will raise any error that occures except ZeroDivisionError.

We can also reverse the situation and ignore any exception except ZeroDivisionError by setting the raise_when parameter. You can understand this as a blacklist:

@makesafe(return_entire_result = True, raise_when = [ZeroDivisionError])
def divide(a, b):
    return a / b

print("Let's calculate!")
result = divide("1", 1)
if result:
    print(result())

Keep in mind that you can not set both ignore and raise_when. If you do so, a TypeError gets raised.

Other Parameters

quiet

refrains displaying the exception

type: bool

default: False

title

text that gets displayed above the exception

type: str

default: "Ignoring exception in {function.__name__}"

colored

displays the exception in a darker color; may not work on every device / console; should not be used when using a file for the output

type: bool

default: False

file

a file or file-like object where the ouput gets written to

type: typing.TextIO

default: sys.stderr

inspired by discord.py

Tips

In case you want to just run a function safely instead of directly making it safe, you can include this function:

from safefunc import makesafe

def runsafe(function, *args, **kwargs):
    return makesafe(*args, **kwargs)(function)