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This calculator runs entirely in your terminal and supports the four basic arithmetic operations. What sets it apart from a one-shot calculator is persistence: every successful calculation is appended to history.txt, so you can review past results at any time during your session or across sessions.
How to run
python3 Calculator_With_History.py
Calculation-> prompt, enter either a math expression or one of the built-in commands.
Calculations
Use the format <number> <operator> <number>, with spaces between each part.
| Component | Details |
|---|
| Numbers | Any integer or decimal (e.g., 5, 3.14) |
| Operators | + (add), - (subtract), * (multiply), / (divide) |
| Example inputs | 5 + 3, 10 / 2, 7.5 * 4, 100 - 33 |
Commands
| Command | What it does |
|---|
History | Prints all saved calculations, newest first |
Clear | Wipes the contents of history.txt |
Quit | Exits the program |
.capitalize() internally, so history, HISTORY, and History all work.
Terminal session example
------------- CALCULATOR -----------------
Calculation-> ( + - / * ) OR COMMAND (History, Clear, Quit): 5 + 3
Result: 8
Calculation-> ( + - / * ) OR COMMAND (History, Clear, Quit): 10 / 2
Result: 5
Calculation-> ( + - / * ) OR COMMAND (History, Clear, Quit): 7.5 * 4
Result: 30
Calculation-> ( + - / * ) OR COMMAND (History, Clear, Quit): History
7.5 * 4=30
10 / 2=5
5 + 3=8
Calculation-> ( + - / * ) OR COMMAND (History, Clear, Quit): Clear
History cleared!
Calculation-> ( + - / * ) OR COMMAND (History, Clear, Quit): Quit
How history works
Each successful calculation is saved to history.txt in the directory where you ran the script. Entries are written one per line using the format:
For example:
5 + 3=8
10 / 2=5
7.5 * 4=30
History command, entries are printed in reverse order (newest first) so the most recent calculation is always at the top. If no calculations have been saved yet, the program prints "No history yet!". If the file does not exist at all, it prints "No history file found!".
history.txt is created relative to your current working directory, not the script’s location. If you run the script from different directories, each directory gets its own separate history.txt file.
Error handling
| Situation | Message printed |
|---|
Division by zero (e.g., 5 / 0) | Error! Division by zero is not allowed. |
Wrong number of parts (e.g., 5 +) | Invalid format! Use: number operator number |
Non-numeric input (e.g., abc + 3) | Invalid input! Please enter valid numbers. |
Unsupported operator (e.g., 5 ^ 3) | Invalid operator! Use +, -, *, or / |