Powershell implementation of vex (virtualenv manager)

vex.ps1

[CmdletBinding(DefaultParameterSetName="ByName")]
Param (

  [Parameter(Position=0, Mandatory=$true, ParameterSetName="ByName")]
  [String]
  $VE,

  [Parameter(Position=1)]
  [ScriptBlock]$sb,

  [Parameter(Mandatory=$true, ParameterSetName="ByPath")]
  [String]
  $Path,

  [Switch]$Make,
  [Switch]$Remove,
  [Switch]$Temp,

  [String]$CWD
)

# -Path pathname ($ve is $venvroot/$ve)
# -Make creates first
# -Remove removes after
# -Temp creates and removes
# -Cwd changes directory
#
# Not implemented yet
# --venv use python -m venv instead of virtualenv
# --python python executable
# --config config file
#
# If $sb is empty, open a nested prompt

$venvroot = (Resolve-Path "~/.virtualenvs").Path

# A temporary VE is made at start and removed at end
if ($Temp) {
    $Make = $true
    $Remove = $true
}

# A named VE is stored in $venvroot
if ($PsCmdlet.ParameterSetName -eq "ByName") {
    $Path = (Join-Path $venvroot $VE)
}

if ($Make) {
    # Make sure the virtualenv does not already exist
    if (Test-Path -PathType Container $Path) {
        throw "Directory $Path already exists"
    }
    # If $venvroot doesn't exist, create it
    if (($PsCmdlet.ParameterSetName -eq "ByName") -and ! (Test-Path -PathType Container $venvroot)) {
        $null = New-Item -Type Directory $venvroot
    }
    # Make the virtualenv
    virtualenv $Path
}

# Check the virtualenv exists
if (! (Test-Path -PathType Container $Path)) {
    throw "Virtualenv $Path does not exist"
}

# Work out the full pathname, the Scripts directory and the location of Python
$Path = (Resolve-Path $Path).Path
$scripts = (Join-Path $Path Scripts)
$python = (Join-Path $scripts python.exe)

if (! (Test-Path -PathType Leaf $python)) {
    throw "Virtualenv $Path does not exist"
}


$oldpath = $env:PATH
$oldvenv = $env:VIRTUAL_ENV
if ($cwd) { pushd $cwd }
try {
    $env:PATH = $scripts + ';' + $env:PATH
    $env:VIRTUAL_ENV = $Path
    if ($sb) { & $sb } else { $host.EnterNestedPrompt() }
}
finally {
    if ($cwd) { popd }
    $env:PATH = $oldpath
    $env:VIRTUAL_ENV = $oldenv
}

# Remove the virtualenv if requested
if ($Remove) {
    Remove-Item -Recurse $Path
}