Allow boolean flags to work without passing True

[williamFalcon]

We tried to fix this but it's still broken

This fails when adding args to argparse automatically...

--auto_lr_find

Instead we have to do:

--auto_lr_find True

which is not great

[SkafteNicki]

This only seems to be a problem with the auto_lr_find flag, since it is the only argument that is a union between the 4 allowed types (str, float, int, bool) in the add_argparse_args. So either this needs to be handled as a special case in the argparser or remove one of its allowed value (str or bool).

[williamFalcon]

it's a problem for many flags haha. The pattern is bool or the callback or string.

So, early stopping, checkpoint, etc... all have this problem.
And for the batch size and lr finder stuff we have a few options

auto_lr_find=True
auto_lr_find='some.path'

But True is getting parsed as a string which breaks everything.

[williamFalcon]

I think we need to solve this before 0.7.6 release as this is causing a lot of unexpected behaviors @Borda.

Basically i think we need to:

1. allow the flag to be passed in with set_true --my_flag (this becomes a bool with True)
2. but if there is something else, then treat that thing as a string --my_flag this_is_a_string

[Borda]

I think that the complication comes with
https://github.com/PyTorchLightning/pytorch-lightning/blob/236c1378f94a7f9d2e1e205035d4d76733c8f4c9/pytorch_lightning/trainer/trainer.py#L131
so you cannot in argparse define to be store_true and optional string at the same time

[Borda]

well this is the minimal solution

import argparse
p = argparse.ArgumentParser()
p.add_argument("--a", type=str, default=False, nargs="?")
v = vars(p.parse_args())
v = {k: True if v is None else v for k, v in v.items()}
print(v)

gives:

• python sample.py --a >> {'a': True}
• python sample.py >> {'a': False}
• python sample.py --a park >> {'a': 'park'}

[williamFalcon]

let's merge this asap for 0.7.6

[Borda]

let's merge this asap for 0.7.6

ready to review... ^^ @williamFalcon