UPGRADING.md

# 2.0.0 Migration Guide

The 2.0 release of `google-api-python-client` is a significant upgrade as only
python 3.6 and newer is supported. If you are not able to upgrade python, then
please continue to use version 1.x as we will continue supporting python 2.7+ in
[v1](https://github.com/googleapis/google-api-python-client/tree/v1).

In addition, discovery documents will no longer be retrieved dynamically when
you call  `discovery.build()`. The discovery documents will instead be retrieved
from the client library directly. Existing code written for earlier versions of
this library will not require updating. We believe this new default behaviour
will provide a more predictable experience for users. If always using the latest
version of a service definition is more important than reliability, users should
set the `static_discovery` argument of `discovery.build()` to `False` to
retrieve the service definition from the internet.

If you experience issues or have questions, please file an [issue](https://github.com/googleapis/google-api-python-client/issues).

## Supported Python Versions

> **WARNING**: Breaking change

The 2.0.0 release requires Python 3.6+, as such you must upgrade to Python 3.6+
to use version 2.0.0.

## Method Calls

**Note**: Existing code written for earlier versions of this library will not
require updating. You should only update your code if always using the latest
version of a service definition is more important than reliability.

> **WARNING**: Breaking change

The 2.0.0 release no longer retrieves discovery documents dynamically on each
call to `discovery.build()`. Instead, discovery documents are retrieved from
the client library itself.

Under the hood, the `discovery.build()` function retrieves a discovery artifact
in order to construct the service object. The breaking change is that the
`discovery.build()` function will no longer retrieve discovery artifacts
dynamically. Instead it will use service definitions shipped in the library.


**Before:**
```py
from googleapiclient.discovery import build

# Retrieve discovery artifacts from the internet
with build('drive', 'v3') as service:
    # ...
```

**After:**
```py
from googleapiclient.discovery import build

# Retrieve discovery artifacts from the client library
with build('drive', 'v3') as service:
    # ...

# Retrieve discovery artifacts from the internet
with build('drive', 'v3', static_discovery=False) as service:
    # ...
```