3. An Informal Introduction to Python — Python v2.7.2 documentation

In the following examples, input and output are distinguished by the presence or absence of prompts (>>> and …): to repeat the example, you must type everything after the prompt, when the prompt appears; lines that do not begin with a prompt are output from the interpreter. Note that a secondary prompt on a line by itself in an example means you must type a blank line; this is used to end a multi-line command. Many of the examples in this manual, even those entered at the interactive prompt, include comments. Let’s try some simple Python commands. 3.1.1. The interpreter acts as a simple calculator: you can type an expression at it and it will write the value. The integer numbers (e.g. 2, 4, 20) have type int, the ones with a fractional part (e.g. 5.0, 1.6) have type float. The return type of a division (/) operation depends on its operands. With Python, it is possible to use the ** operator to calculate powers : >>> 5 ** 2 # 5 squared25>>> 2 ** 7 # 2 to the power of 7128 3.1.2. See also

PEP 8 -- Style Guide for Python Code Code should be written in a way that does not disadvantage other implementations of Python (PyPy, Jython, IronPython, Cython, Psyco, and such).For example, do not rely on CPython's efficient implementation of in-place string concatenation for statements in the form a += b or a = a + b. This optimization is fragile even in CPython (it only works for some types) and isn't present at all in implementations that don't use refcounting. In performance sensitive parts of the library, the ''.join() form should be used instead.

6. Built-in Exceptions — Python v3.1.3 documentation In Python, all exceptions must be instances of a class that derives from BaseException. In a try statement with an except clause that mentions a particular class, that clause also handles any exception classes derived from that class (but not exception classes from which it is derived). Two exception classes that are not related via subclassing are never equivalent, even if they have the same name. The built-in exceptions listed below can be generated by the interpreter or built-in functions. Except where mentioned, they have an “associated value” indicating the detailed cause of the error. This may be a string or a tuple containing several items of information (e.g., an error code and a string explaining the code). User code can raise built-in exceptions. The built-in exception classes can be sub-classed to define new exceptions; programmers are encouraged to at least derive new exceptions from the Exception class and not BaseException. exception BaseException exception Exception