basic-calculator

Really simple, limited calculator. Two numbers are read, one of four operations is chosen, and the result is printed.

Requirements

Python 2. The program uses raw_input and print statements, so it is rejected at parse time by Python 3 and does not run there at all. It has been verified under Python 2.7.18.

Which interpreter this project should target going forward is an open question — see issue #1.

Run

python calculator.py

Four things are read from standard input, in this order: the first number, the second number, the operation, and a final line that dismisses the exit prompt.

All four are required, including the last. An unattended run that supplies fewer than four lines waits at whichever prompt it reached for as long as standard input stays open, and raises EOFError once it closes — so omitting only the fourth line still prints the answer first and fails afterwards. Wrapping such a run in timeout is advisable.

Operations

The operation is matched case-insensitively against exactly these four words, spelled as the prompt spells them:

Type	Result
Add	the two numbers added
Subract	the second number subtracted from the first
Multiply	the two numbers multiplied
Divide	the first number divided by the second, followed by the remainder

Note the spelling of Subract — the correctly-spelled subtract is not accepted and falls through to That wasn't an option.. This is tracked in issue #7.

Anything else prints That wasn't an option. and exits. Surrounding whitespace is not stripped, so a stray leading or trailing space is also rejected.

Example

Transcript of a real run under Python 2.7.18. Input was piped rather than typed, which is why the three prompts appear on one line with no echoed answers:

$ printf '6\n3\nadd\n\n' | python calculator.py
What is the first number? What is the second number? Add, Subract, Multiply or Divide? The answer is  9.0

Press Enter to exit.

The Divide branch additionally reports the remainder:

$ printf '7\n2\ndivide\n\n' | python calculator.py
What is the first number? What is the second number? Add, Subract, Multiply or Divide? The answer is  3.5  with  1.0  left over.

Press Enter to exit.

Known limitations

All of the following were reproduced under Python 2.7.18 and are tracked as issues:

• A second number of 0 with Divide raises ZeroDivisionError instead of printing a message (#5).
• Non-numeric text at either number prompt raises ValueError and exits, with no chance to retry (#6).
• Both operands are floats, so Divide reports a true-division quotient and a float remainder — the same leftover twice (#8).

License

Stephenson Software Non-Commercial License. See LICENSE.