kivy : The term 'kivy' is not recognized as cmdlet name, function, script file or operable program

Question

When trying to run script

from kivy.app import App
from kivy.uix.gridlayout import GridLayout
from kivy.uix.label import Label
from kivy.uix.textinput import TextInput

class TelaLogin(GridLayout):
    def __init__(self, **kwargs):
        super(TelaLogin, self).__init__(**kwargs)
        self.cols = 2
        self.add_widget(Label(text='Usuário'))
        self.username = TextInput(multiline=False) 
        self.add_widget(self.username)
        self.add_widget(Label(text='Senha'))
        self.password = TextInput(password=True, multiline=False)
        self.add_widget(self.password)
class MyApp(App):
    def build(self):
        return TelaLogin()

if __name__ == '__main__':
    MyApp().run()

To execute the command placed > kivy main.py

I get the following error

kivy : O termo 'kivy' não é reconhecido como nome de cmdlet, função, arquivo de script ou programa operável. Verifique a grafia do nome ou, se um caminho tiver     
sido incluído, veja se o caminho está correto e tente novamente.
No linha:1 caractere:1
+ kivy main.py
+ ~~~~
    + CategoryInfo          : ObjectNotFound: (kivy:String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException