Creating a DateEntry widget

Let's try creating a validating version of our Date field. We'll make a DateEntry widget that prevents most erroneous keystrokes, then checks for date validity on focusout. If the date is invalid, we'll mark the field in some way and display an error. Let's perform the following steps to do the same:

  1. Open a new file called DateEntry.py and begin with the following code:
from datetime import datetime

class DateEntry(ttk.Entry):
    """An Entry for ISO-style dates (Year-month-day)"""

    def __init__(self, parent, *args, **kwargs):
        super().__init__(parent, *args, **kwargs)
        self.config(
            validate='all',
            validatecommand=(                self.register(self._validate),                '%S', '%i', '%V', '%d' ), invalidcommand=(self.register(self._on_invalid), ...

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