if len(entry_object.get()) == 0:  # empty!
    # do something

if not entry_object.get(): # empty! (empty string is false value)
    # do something

for entry in entry_list:
    if not entry_object.get():
        # empty!

entry_list = []

entry = Entry(...)
...
entry_list.append(entry)

entry = Entry(...)
...
entry_list.append(entry)

entry_list = [child for child in root_widget.winfo_children()
              if isinstance(child, Entry)]