ex37.txt

Symbol Review (and learning)


*************
Keywords (re-ordered from Zed's list to group related terms)
*************

and - Boolean comparison; note order of evaluation (from Pydoc): "The expression ``x and y`` first evaluates *x*; if *x* is false, its value is returned; otherwise, *y* is evaluated and the resulting value is returned."

or - Boolean comparison; note order of evaluation (from Pydoc): "The expression ``x or y`` first evaluates *x*; if *x* is true, its value is returned; otherwise, *y* is evaluated and the resulting value is returned."

not - Boolean negation operator

del - deletes contents of a target list *recursively*

while - loop until condition is true

for - first keyword of an iterator

break - appears in body of for or while loops

global - instantiates a global variable (global to script and where it's included); gets tricky with exec statements and eval() function

with - invokes a context manager (what's that?) before executing a statement block; benefits include "allow[ing] common ``try``...``except``...``finally`` usage patterns to be encapsulated for convenient reuse."

assert - debugging expression, only executed if a debugging context (if I have that notion correct) is active.

if - conditional

elif - Python's way of writing 'else if'

else - fallthrough for if control block; usable in if blocks as well as try blocks

pass - null placeholder for use when building code and you don't know what will go in a function definition but you do know that you want a particular function or kind of function; probably very useful for TDD; not the same as an empty return because flow continues after the pass statement; see also http://stackoverflow.com/questions/7872611/in-python-what-is-the-difference-between-pass-and-return

yield - used in the body of a generator function definition; (what's a generator function?)

import - primary keyword to include Python modules or specific pieces of them

from - secondary keyword for importing specific pieces of Python modules

as - tertiary keyword for importing Python modules or specific pieces of them

print - echo to screen or other output

class - keyword for defining a Python class

exec - [not clear at all what this does; I can see that it executes code, but it's not obvious to me why or when you would use it]

in - indicates where to look for preceding variable; part of iterator

continue - skips to the next cycle of a for or while loop

try - start of a control block containing statements with expectation of occasional failure

except - Python word for 'catch'; used in try . . . except . . . finally blocks; try block can contain multiple except clauses

finally - cleanup handler for try block

raise - throws an exception

is - test for object identity (NOT equality)

return - send value back to calling statement

def - keyword indicating that a function definition is to follow

lambda - shorthand for creating anonymous functions; lambda arguments: expression is the same as def name( arguments ): return expression [properly indented, of course]

*************
Data Types
*************

True - constant

False - constant

None - constant representing null

strings - concatenated collections of characters that can be manipulated in certain ways and not in others

numbers - 1, 0, 1000000000035; figure that is a round integer; range unknown

floats - figure that includes a decimal point; does not have to have non-zero values in the fractional places; 53 bits of precision (there's also a decimal module if greater precision is needed), range unknown; 10.0, 3.141579, 22/7

lists - collections of data types, including tuples and lists


*************
String Escape Sequences
*************

\\	Allows a slash
\'	Allows a single quote
\"	Allows a double quote
\a	ASCII bell character (calls a simple sound from the OS)
\b	ASCII backspace; not sure why I would use this except in some textual deformation
\f	ASCII form feed; functionally, seems to just add a newline, but technically I think it is a page break
\n	ASCII line feed; adds new line between appearance of character
\r	ASCII carriage return
\t	Tab
\v	ASCII vertical tab; drops down to the next line and continues


*************
String Formats
*************

%d	signed integer decimal (rounds, but be careful of precision flaws)
%i	signed integer decimal (rounds, but be careful of precision flaws)
%o	unsigned octal; inserts leading 0 if not exists
%u	unsigned decimal (rounds)
%x	unsigned hex (lowercase); inserts leading 0x if leading character not already 0
%X	unsigned hex (uppercase); inserts leading 0X if leading character not already 0
%e	floating point exponential format (lowercase)
%E	floating point exponential format (uppercase)
%f	floating point decimal
%F	floating point decimal
%g	Floating point format. Uses exponential format if exponent is greater than -4 or less than precision, decimal format otherwise.
%G	Floating point format. Uses exponential format if exponent is greater than -4 or less than precision, decimal format otherwise.
%c	single character
%r	Converts to sting using repr(); inter alia, will include demarcating quotes in the result as if they were part of the string
%s	Formats as a string using str()
%%	Allows insertion of percentage symbol, but it seems like you can't use it in isolation, needs some other formatted item before it


*************
Operators
*************

+	Addition, concatenation
-	Subtraction only
*	Multiplication
**	Exponent
/	Division
//	"Floor Division - The division of operands where the result is the quotient in which the digits after the decimal point are removed." (from http://www.tutorialspoint.com/python/python_basic_operators.htm); a/k/a division in which the result is the closest whole number
%	Modulo
<	Less than
>	Greater than
<=	Less than or equal to
>=	Greater than or equal to
==	Equality test
!=	Not equal to
<>	Greater than or less than; strongly similar to !=
( )	Tuple designator; tuples cannot be edited
[ ]	List designator; NB: a list can be converted to a set, which has different properties than a list
{ }	Dictionary designator
@	
,	Separator for items in a list or key-value pairs in a dictionary
:	Declares the start of an indented block; separates a key from its value in a dictionary
.	Delimiter for class methods; NB: not concatenation
=	Assignment
;	Separates statements to permit multiple on one line
+=	Unary addition+assignment; a/k/a increment
-=	Unary subtraction+assignment; a/k/a decrement
*=	Unary multiplication+assignment
/=	Unary division+assignment
//=	Unary floor division+assignment
%=	Unary modulo+assignment
**=	Unary exponent+assignment