How do I activate a virtualenv inside PyCharm's terminal?

Edit:

According to https://www.jetbrains.com/pycharm/whatsnew/#v2016-3-venv-in-terminal, PyCharm 2016.3 (released Nov 2016) has virutalenv support for terminals out of the box

Auto virtualenv is supported for bash, zsh, fish, and Windows cmd. You can customize your shell preference in Settings (Preferences) | Tools | Terminal.

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Old Method:

Create a file .pycharmrc in your home folder with the following contents

source ~/.bashrc
source ~/pycharmvenv/bin/activate

Using your virtualenv path as the last parameter.

Then set the shell Preferences->Project Settings->Shell path to

/bin/bash --rcfile ~/.pycharmrc

Update:

The preferences in Settings (Preferences) | Tools | Terminal are global.
If you use a venv for each project, remember to use current path variable and a default venv name:

"cmd.exe" /k ""%CD%\venv\Scripts\activate"" 

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For Windows users: when using PyCharm with a virtual environment, you can use the /K parameter to cmd.exe to set the virtual environment automatically.

PyCharm 3 or 4: Settings, Terminal, Default shell and add /K <path-to-your-activate.bat>.

PyCharm 5: Settings, Tools, Terminal, and add /K <path-to-your-activate.bat> to Shell path.

PyCharm 2016.1 or 2016.2: Settings, Tools, Terminal, and add ""/K <path-to-your-activate.bat>"" to Shell path and add (mind the quotes). Also add quotes around cmd.exe, resulting in:

"cmd.exe" /k ""C:\mypath\my-venv\Scripts\activate.bat""

For Windows users when using PyCharm and a virtual environment under Windows, you can use the /k parameter to cmd.exe to set the virtual environment automatically.

Go to Settings, Terminal, Default shell and add /K <path-to-your-activate.bat>.

I don't have the reputation to comment on the earlier response so posting this corrected version. This really saves a LOT of time.

Update:

Note: Pycharm now supports virtual environments directly and it seems to work well for me - so my workaround not needed anymore.