Python
after we've added options (in parser)
(options, args) = parser.parse_args()
argv
- argument variable - variable holds arguments passed to script when running it script, first, second, third = argv (line 3) - script = name of python script - first, second, third = 3 variables arguments assigned to
open()
- function opens a file - Required argument is filename - Default access_mode is read(r) - Does not return actual content; creates/reads fileObject -
close()
- method flushes unwritten information and closes file object - Not necessary, but important best practice
read()
- method reads a string from an open file - fileObject.read([count]) - Count = # of bytes to read, reads as much as possible if not given
Boolean tests should be..
...simple. If complex, move calculations to variables earlier in function and use a good name for the variable.
Treat if statements like...
..paragraphs. Each if, elif, and else grouping is like a set of sentences. Put blank lines before and after.
Never nest if-statements more than..
..two deep. Try to do one deep (put inside another function).
How many characters to a line?
80 characters
compound data type
A data type that is itself made up of elements that are themselves values.
lambda
A piece of code which can be executed as if it were a function but without a name. (It is also a keyword used to create such an anonymous function.)
\b
ASCII Backspace (BS) - Erases last character printed
\a
ASCII Bell -may cause receiving device to emit a bell or warning of some kind
\r
ASCII Carriage Return (CR) - Resets position to beginning of a line of text
\f
ASCII FormFeed (FF) - ASCII Control character. Forces printer to eject current page and continue printing at top of another.
\t
ASCII Horizontal Tab (TAB) - 8 horizontal spaces; tab
\n
ASCII LineFeed (LF) - Goes to next line -newline escape
\v
ASCII Vertical Tab (VT) - 6 vertical lines; 1 inch
append()
Adds input to the end of a list
input()
Assumes input is valid python expression, returns evaluated result
int()
Convert a string to an integer int(raw_input(> ))
%s
Converts String (converts any Python object using str())
%d
Converts a signed integer decimal
def
Defines a function def function1(): print "this is function 1"
truncate()
Empties the file
%F
Floating point decimal format (UPPERCASE)
%f
Floating point decimal format (lowercase)
%e
Floating point exponential format (lowercase)
%E
Floating point exponential format (uppercase)
universal import
Imports all functions and variables from a module - Can cause conflicts with user defined functions and vars - Better to import only necessary functions from module import *
my_list.insert(4, "cat")
Inserts the string "cat" at the 4th position in a list
%d
Integer format character
{}.format(something)
Is the new string.format in Python 3. This is how indexing works: "My first name is {0} and my last name is {1}. You can call me {0}".format("John","Doe").
What is sys.argv?
It allows you to input parameters from the command line.
split()
Method splits a string into separate phrases - Default is to split on whitespace split(str, num) str = separator (optional) numb = number of separations (optional)
aliases
Multiple variables that contain references to the same object.
The first input operation is called the _____, and its purpose is to get the first input value that will be tested by the validation loop.
Priming read
raw_input()
Raw input prompts the user for an input and then turns that input into a string. In between "(" and ")" the programmer writes the prompt that will prompt the user. When you set raw_input() equal to a variable, that variable becomes what the user inputs.
raw_input('prompt:')
Reads a line of input from user and returns as string
readline()
Reads one line of text file
len(input)
Return the number of items from a sequence or characters in a string
exists()
Returns TRUE if file in argument exists, FALSE if not
%G
Same as "E" if exponent is greater than -4 or less than precision
%g
Same as "e" if exponent is greater than -4 or less than precision
A(n) ?? is a special value that marks the end of a sequence of items.
Sentinel
%c
Single character -accepts integer or single char string
sorted()
Sorts a list from smallest to highest or a string alphabetically sorted(str, reverse=True) <- Sorts backwards
Cardinal Numbers
Start at 0
Ordinal Numbers
Start at 1; First, second, third
%s
String -Converts any python object using str()
%r
String -converts any python object using repr()
%r
String (converts any Python object using repr())
%s
String format character; use for user formatting
len[2] = 3
The 2nd term of the list is now equal to 3
trace
To follow the flow of execution of a program by hand, recording the change of state of the variables and any output produced.
%X
Unsigned Hexadecimal (uppercase)
%x
Unsigned hexadecimal (lowercase)
<>
Value of two operands not equal? -Similar to !=
function parameter
Variable name for passed in argment def function(parameter):
write(stuff)
Writes stuff to file
list_name.append("")
appends thing to lists
lower()
converts a string to lowercase
upper()
converts a string to uppercase
raise
create a user defined exception
%r is used for...
debugging and display
del
deletes objects
Else must have a...
die function that prints out an error message, in case the else doesn't make sense. Shows errors.
%s is used for
display
pass
does nothing
Every if statement must have a(n)...
else
\
escape; tells python to ignore following character, or puts difficult characters into strings when used with specific *escape sequences*
exec
executes Python code dynamically
len(my_list)
finds the length of a list
After the execution of the following statement, the variable sold will reference the numeric literal value as a(n) _____ data type: sold = 256.752
float
from
for importing a specific variable, class or a function from a module
my_list[:]
gives you the entire list
my_list[-1]
gives you the last term in the list
my_list[1:3]
gives you the list starting at the 1st position and ending at the 2nd position
my_list[0:]
gives you the whole list, starting at the 0 position
as
if we want to give a module a different alias
The _____ built-in function is used to read a number that has been typed on the keyboard.
input()
Syntax to index 2 nested lists?
list[x][y]
\b
matches a word boundar
\d
matches any numeric digit
^
matches the beginning of a string
$
matches the end of a string
pop()
method removes and returns the last object from a list
\n
moves whatever's after it to a new ling
%
no argument converted, results in "%" in the result
adding parser options
parser.add_option('-n, '--new')
.remove()
removes items from list
%d
signed integer decimal
%i
signed integer decimal
my_list.sort()
sorts a list from lowest to highest, or alphabetical
\t
tab character
%u
unsigned decimal
%o
unsigned octal
assert
used for debugging purposes
continue
used to interrupt the current cycle, without jumping out of the whole cycle. New cycle will begin.