Since Google has shut down its weather API, I suggest to check out OpenWeatherMap:

The OpenWeatherMap service provides free weather data and forecast API suitable for any cartographic services like web and smartphones applications. Ideology is inspired by OpenStreetMap and Wikipedia that make information free and available for everybody. OpenWeatherMap provides wide range of weather data such as map with current weather, week forecast, precipitation, wind, clouds, data from weather Stations and many others. Weather data is received from global Meteorological broadcast services and more than 40 000 weather stations.

It's not a Python library, but it's super easy to use, because you can get results in JSON format.

Here's an example using Requests:

>>> from pprint import pprint
>>> import requests
>>> r = requests.get('http://api.openweathermap.org/data/2.5/weather?q=London&APPID={APIKEY}')
>>> pprint(r.json())
{u'base': u'cmc stations',
 u'clouds': {u'all': 68},
 u'cod': 200,
 u'coord': {u'lat': 51.50853, u'lon': -0.12574},
 u'dt': 1383907026,
 u'id': 2643743,
 u'main': {u'grnd_level': 1007.77,
           u'humidity': 97,
           u'pressure': 1007.77,
           u'sea_level': 1017.97,
           u'temp': 282.241,
           u'temp_max': 282.241,
           u'temp_min': 282.241},
 u'name': u'London',
 u'sys': {u'country': u'GB', u'sunrise': 1383894458, u'sunset': 1383927657},
 u'weather': [{u'description': u'broken clouds',
               u'icon': u'04d',
               u'id': 803,
               u'main': u'Clouds'}],
 u'wind': {u'deg': 158.5, u'speed': 2.36}}

And here's an example using PyOWM, a Python wrapper around the OpenWeatherMap web API:

>>> import pyowm
>>> owm = pyowm.OWM()
>>> observation = owm.weather_at_place('London,uk')
>>> w = observation.get_weather()
>>> w.get_wind()
{u'speed': 3.1, u'deg': 220}
>>> w.get_humidity()
76

The official API documentation is available here.

To get the API key sign up to open weather map here