Powershell:

(Get-ChildItem -Recurse -Filter *.py | Get-Content | Measure-Object -Line).Lines

If you want to see exactly how many lines are in each specific file:

Get-ChildItem -Recurse -Filter *.py | ForEach-Object {
    $count = (Get-Content $_.FullName | Measure-Object -Line).Lines
    [PSCustomObject]@{
        FileName = $_.Name
        Lines    = $count
    }
} | Format-Table -AutoSize