Date & Time (datetime): The Standard Way to Handle Time Data

What might confuse you right now

"Isn't time just a string? Why make it an object?"

Strings can display time, but they can't reliably compute with it. Comparisons, arithmetic, and format conversions all need datetime objects.

One-line definition

datetime provides time creation, parsing, formatting, and arithmetic.

Real-life analogy

A handwritten calendar can be read but can't do math. A digital calendar auto-reminds and calculates.

Minimal runnable example

from datetime import datetime, timedelta

now = datetime.now()
print(now.strftime("%Y-%m-%d %H:%M:%S"))

deadline = now + timedelta(days=7)
print(deadline.strftime("%Y-%m-%d"))

String to datetime

dt = datetime.strptime("2026-02-11 09:30", "%Y-%m-%d %H:%M")
print(dt)

Quick quiz (5 min)

1. Print the current time, formatted.
2. Calculate the date 30 days from now.
3. Write a function that returns how many days remain until a deadline.

Quiz answer guidelines & grading criteria

• Answer direction: working code that covers core conditions and edge inputs from the prompt.
• Criterion 1 (Correctness): Main flow produces correct results, key branches execute.
• Criterion 2 (Readability): Clear variable names, no excessive nesting.
• Criterion 3 (Robustness): Basic protection against null values, type errors, or unexpected input.

Transfer task (homework)

Build a "task deadline reminder": input a due date, output remaining days and status.

Acceptance criteria

You can independently:

• Parse and format time strings
• Use timedelta for time arithmetic
• Avoid comparing time via raw strings

Common errors & debugging steps (beginner edition)

• Can't understand the error: read the last line for the error type (e.g., TypeError, NameError), then trace back to the relevant code line.
• Not sure about a variable's value: temporarily add print(variable, type(variable)) at key points to verify data matches expectations.
• Code changes aren't taking effect: confirm the file is saved, you're running the right file, and your terminal environment (venv) is correct.

Common misconceptions

• Misconception: Comparing time strings directly works fine.
• Reality: Convert to datetime first, then compare.