Ch 5 introduces Python — its features, installation, IDLE environment, variables, data types (including complex), operators, expressions, type conversion, and input/output functions.
Python features: interpreted, high-level, dynamic typing, automatic memory management, extensive standard library, cross-platform, open source. Modes: interactive (>>> prompt, immediate execution) and script (save as .py, run together). IDLE: Integrated Development and Learning Environment — colour-coded syntax, auto-indent, debugger. Tokens: keywords (reserved: if, while, def, class, import — 35 total), identifiers (names you choose), literals (fixed values), operators, punctuators.
Variables: dynamically typed — type determined at runtime. id(x) returns memory address. Data types: int (no size limit in Python 3!), float (64-bit double precision), complex (3+4j), str ("hello"), bool (True/False), None. Type conversion: implicit (int → float in mixed arithmetic) and explicit (int(), float(), str()). Operators: arithmetic (+, -, *, /, //, %, **), relational (==, !=, <, >, <=, >=), logical (and, or, not), assignment (=, +=, -=, etc.), identity (is, is not), membership (in, not in). Precedence: ** → unary → *, /, //, % → +, - → relational → not → and → or.
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In Python, the type of a variable is determined at runtime, not during compilation. You don't declare types explicitly: x = 5 makes x an int; later x = "hello" makes x a str — perfectly valid. The type is associated with the value, not the variable name. This makes Python flexible and concise, but requires careful programming. Use type(x) to check a variable's type at any point. Contrast with C/Java where int x = 5 locks x to integer type.
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