App Calling & Return Values

In this section, we'll take a closer look at the App.__call__() method.

Input Command

Typically, a Cyclopts app looks something like:

app = cyclopts.App()


@app.command
def foo(a: int, b: int, c: int):
    print(a + b + c)


app()

$ my-script 1 2 3
6

App.__call__() takes in an optional input that it parses into an action. If not specified, Cyclopts defaults to sys.argv[1:], i.e. the list of command line arguments. An explicit string or list of strings can instead be passed in.

app("foo 1 2 3")
# 6
app(["foo", "1", "2", "3"])
# 6

If a string is passed in, it will be internally converted into a list using shlex.split.

Return Value

The app invocation returns the value of the called command.

app = cyclopts.App()


@app.command
def foo(a: int, b: int, c: int):
    return a + b + c


return_value = app("foo 1 2 3")
print(f"The return value was: {return_value}.")
# The return value was: 6.

If you decide you want each command to return an exit code, you could invoke your app like:

if __name__ == "__main__":
    sys.exit(app())

Exception Handling and Exiting

For the most part, Cyclopts is hands-off when it comes to exiting the application. However, by default, if there is a Cyclopts runtime error, like CoercionError or a ValidationError, then Cyclopts will perform a sys.exit(1). This is to avoid displaying the unformatted, uncaught exception to the CLI user. This can be disabled by specifying exit_on_error=False when calling the app. At the same time, you may want to set print_error=False to disable the printing of the formatted exception.

app("this-is-not-a-registered-command")
print("this will not be printed since cyclopts exited.")
# ╭─ Error ─────────────────────────────────────────────────────────────────────╮
# │ Unable to interpret valid command from "this-is-not-a-registered-command".  │
# ╰─────────────────────────────────────────────────────────────────────────────╯

app("this-is-not-a-registered-command", exit_on_error=False, print_error=False)
# Traceback (most recent call last):
# File "<stdin>", line 1, in <module>
# File "/cyclopts/cyclopts/core.py", line 318, in __call__
#   command, bound = self.parse_args(tokens)
#                    ^^^^^^^^^^^^^^^^^^^^^^^
# File "/cyclopts/cyclopts/core.py", line 281, in parse_args
#   command, bound, unused_tokens = self.parse_known_args(tokens)
#                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
# File "/cyclopts/cyclopts/core.py", line 246, in parse_known_args
#   raise InvalidCommandError(unused_tokens=unused_tokens)
# cyclopts.exceptions.InvalidCommandError: Unable to interpret valid command from "this-is-not-a-registered-command".

try:
    app("this-is-not-a-registered-command", exit_on_error=False, print_error=False)
except CycloptsError:
    pass
print("Execution continues since we caught the exception.")

With exit_on_error=False, the InvalidCommandError is raised the same as a normal python exception.