python version manager - a simple version manager with hardcoded paths that can server as a template for future use, Can be used from PS or CMD.

pyvm.cmd

@echo off

(echo REM pyvm.cmd) > "%TEMP%\_env.cmd"
powershell %~dp0\pyvm.ps1 %*

call "%TEMP%\_env.cmd"

pyvm.ps1

#[cmdletbinding()]
param ($command, [Alias("p")][switch][bool]$persistent, [switch][bool]$verbose) 

write-host "pyvm - python version manager"
write-host "command=$command args=$args"

function where-is($wally) {
    cmd /c "where $wally"
    #Get-Command $wally
}

function add-topath($path, [switch][bool] $persistent) {
    $p = $env:Path.Split(';')
    $p = $p | % { $_.trimend("\") }

    $paths = @($path) 
    $paths | % { 
        $path = $_
        write-verbose "adding $path to PATH"
        $p += $path.trimend("\")

    }
    
    $env:path = [string]::Join(";",$p)

    [System.Environment]::SetEnvironmentVariable("PATH", $env:Path, [System.EnvironmentVariableTarget]::Process);
    if ($persistent) {
          write-warning "saving global PATH"
          [System.Environment]::SetEnvironmentVariable("PATH", $env:Path, [System.EnvironmentVariableTarget]::Machine);
    }
}

function remove-frompath($path, [switch][bool] $persistent) {
    $paths = @($path) 
    $p = $env:Path.Split(';')
    $p = $p | % { $_.trimend("\") }
    $paths | % { 
        $path = $_
        $found = $p | ? { $_ -ieq $path }
        if ($found -ne $null) {
            write-verbose "found $($found.count) matches"
            $p = $p | ? { !($_ -ieq $path) }    
        }
    }

    $env:path = [string]::Join(";",$p)

    [System.Environment]::SetEnvironmentVariable("PATH", $env:Path, [System.EnvironmentVariableTarget]::Process);
    if ($persistent) {
        write-warning "saving global PATH"
        [System.Environment]::SetEnvironmentVariable("PATH", $env:Path, [System.EnvironmentVariableTarget]::Machine);
    }
}

function contains-path($path) {
    $paths = @($path) 
    $p = $env:Path.Split(';')
    $p = $p | % { $_.trimend("\") }
    $r = $true
    $paths | % { 
        $path = $_       
        $found = $p | ? { $_ -ieq $path }
        if (@($found).Count -le 0) { 
            write-verbose "$path not found in PATH"
            $r = $false 
        }
        else {
            write-verbose "$path found in PATH"
        }
    }

    return $r
}


$vp = $VerbosePreference
try {
if ($verbose) { $VerbosePreference = "Continue" }


$paths = @{
 python3 =   "c:\tools\python3","C:\tools\python3\scripts"
 python2 =   "c:\tools\python2","C:\tools\python2\scripts"
}



switch($command) {
    "list" {
        write-host "Available python versions"
        $paths.GetEnumerator() | % {
            $active = contains-path $_.Value
            $msg = ""
            if ($active) { $msg += " * " }
            else { $msg += "   " }
            $msg += $_.Key 
            $msg += "  " + $_.Value
            write-host $msg
        }
    }
    "use" {
        if ($args.Length -eq 0) {
            throw "must specify a version"`
        }
        $ver = $args[0]
        switch($ver) {
            { @("3", "python3") -contains $_ } { 
                write-host "using $($paths.python3)"
                $paths.values | % { 
                    write-verbose "removing $_ from path"
                    remove-frompath $_
                    }
                add-topath $paths.python3 -persistent:$persistent
                }
            { @("2", "python2") -contains $_ } { 
                write-host "using  $($paths.python2)"
                $paths.values | % { 
                    write-verbose "removing $_ from path"
                    remove-frompath $_
                }
                add-topath $paths.python2 -persistent:$persistent
            }
            { @("none", "no") -contains $_ } {
                 write-host "disabling python"
                $paths.values | % { 
                    write-verbose "removing $_ from path"
                    remove-frompath $_ -persistent:$persistent
                }
            }
            default {
                throw "unrecognized version"
            }
        }
    }
    default {
        write-verbose "usage: "
        write-verbose " pyvm list"
        write-verbose " pyvm use"
    }
    
}

    write-verbose "PATH="
    write-verbose "`r`n$env:path"
    
} finally {
    $VerbosePreference = $vp
}


"set PATH=$env:PATH" | out-file "$env:TEMP\_env.cmd" -Encoding ascii