PCEP: Computer Programming and Python Fundamentals

What this domain covers

PCEP's first domain checks whether you can read and write short Python snippets built from literals, variables, operators and built-in I/O. Questions are usually single-line expressions where precedence, type or a subtle naming rule decides the answer.

Core rules

• Identifiers are case-sensitive, may contain letters, digits and underscores, but cannot begin with a digit. Keywords such as class, def and None are reserved. myVar, _x2 and 总量 are legal; 2x and my-var are not.
• Literals include integers (0, 1_000), floats (2.0, 1e3), strings, booleans (True, False) and None.
• Operators: + - * / // % **. / always returns a float; // floors toward negative infinity, so -7 // 2 == -4; % follows the sign of the divisor, so -7 % 2 == 1; ** binds tighter than unary minus, so -2 ** 2 == -4.
• Precedence roughly: **, unary, * / // %, + -, comparisons, not, and, or. Parentheses override it.
• input() always returns a str; convert with int() or float() before arithmetic. print(a, b, sep=",", end="") controls separators and line endings.

Worked example

x = input() and the user types 3; then y = 2; print(x * y) outputs 33, not 6. x is the string "3", and str * int repeats the string. Fix it with x = int(input()).

Traps

• = assigns, == compares; using = in an if is a SyntaxError.
• 1 + 2.0 yields 3.0; mixing int and float promotes to float.
• bool("") is False, but bool("0") is True.
• round(2.5) is 2 (banker's rounding), and int("2.5") raises ValueError.