[DOC-FIX] Document the maximum value and legal characters for log_param, log_metric and set_tag

URLS with the issue:

• https://mlflow.org/docs/latest/python_api/mlflow.html#mlflow.log_param
• https://mlflow.org/docs/latest/python_api/mlflow.html#mlflow.log_metric
• https://mlflow.org/docs/latest/python_api/mlflow.html#mlflow.set_tag

Description of proposal:

Document the maximum value and legal characters for log_param, log_metric and set_tag. Note that log_metric’s value is already documented as float.

Tags:

• Apparently there is a 250 character limit for tag keys. See https://github.com/mlflow/mlflow/blob/master/mlflow/utils/validation.py#L31.
• There is a 5000 character limit for tag values. See: https://github.com/mlflow/mlflow/blob/master/mlflow/utils/validation.py#L30.

Sample error messages for set_tag::

• Tag value 'x...' had length 5001, which exceeded length limit of 250
• Tag value 'vv...' had length 5001, which exceeded length limit of 5000

However, there seems to be no limit to a parameter’s key or value.

Metrics:

• MlflowException: Invalid metric name: ‘01: running time in mins’. Names may only contain alphanumerics, underscores (_), dashes (-), periods (.), spaces ( ), and slashes (/)

[dmatrix]

@tmnhat2001 We always welcome contributions, and this is a good first issue to get started. Go for it and follow the example description of parameters in the API docs.

Cheers! Jules

[rafaelvp-db]

@amesar just drop in to confirm if this has been closed - would you be able to close it, if it’s indeed the case? (if it’s not closed I’m happy to contribute)