On the latest version, when I run the Activate.ps1 script to enable the virtualenv, Cmder throws the following error. Virtualenvs work fine on regular PowerShell.

Cannot write to function prompt because it is read-only or constant.
At C:\Code\Python\env-web\Scripts\Activate.ps1:70 char:1
+ function global:prompt {
+ ~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : WriteError: (prompt:String) [], SessionStateUnauthorizedAccessException
    + FullyQualifiedErrorId : FunctionNotWritable

I face the same problem.

Thanks.

I confirm that removing -Options ReadOnly from Set-Item -Path function:\prompt -Value $Prompt -Options ReadOnly.
virtualenv prompt is back.

If anyone don't know where it is, go to vendor/profile.ps1.

I just write more detail.
Hope anyone who face this issue may see my comment and found that line quickly. 🙂

The last cmder added some protection from anything overwriting global:prompt because I was a little concerned about any script running to hijack it.

Fix virtualenv

If you use virtualenv set $env:VIRTUAL_ENV_DISABLE_PROMPT = 1 all it does is print your projects folder, you've already got that in the console anyway. Tested on python 3.6.

$env will do the current process. Set a user env variable or add $env:VIRTUAL_ENV_DISABLE_PROMPT = 1 to user-profile.ps1

Workaround venv

A quick test and python -m venv seems to ignore $env:VIRTUAL_ENV_DISABLE_PROMPT = 1 and it writes the prompt anyway.

So it looks like you have two options;

1. Remove the function global:prompt from activate.ps1
2. Comment out -options readonly from setting the prompt in cmder profile for now and it will let you clobber function:\prompt again.
3. use virtualenv with the above fix.

I'll have to have a think how to accommodate virtualenv. Going to leave this issue open I think until an update is in the works.

Had the same problem, but I was able to fix it with just commenting the -Options ReadOnly portion only, leaving the rest how it was.
But don't know if it is the right way