We're getting close enough to PyCon to look at the weather forecast. You should certainly bring at least a light jacket and gloves; bring a heavier jacket if you're not used to cold temperatures.
According to Frommer's Portable Chicago, the average temperatures in Chicago in March are a high of 44 degF / 7 degC and a low of 28 deg / -1 degC. The temperatures predicted for the week match the averages: high temperatures of about 40-50 degF / 5-10 degC, and night temperatures of around freezing. There are chances of rain on Wednesday night and on Monday, and a chance of light snow on Friday night. Winds are predicted to be moderate, so wind chill is probably not going to make things much colder.
Here's a banner from Weather Underground showing the current conditions for the hotel's postal code: