Section 1
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Else must have a...
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Last updated
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Date created
Mar 1, 2020
Cards (154)
Section 1
(50 cards)
Else must have a...
die function that prints out an error message, in case the else doesn't make sense. Shows errors.
modules
-aka libraries -feature sets you can import into a program
close()
- method flushes unwritten information and closes file object - Not necessary, but important best practice
while
controls flow of the program with truth statements. Statements inside the while loop are executed until the expression evaluates false.
%r
String format character; use for debugging
\t
tab character
**
exponent
%d
Integer format character
exists()
Returns TRUE if file in argument exists, FALSE if not
truncate()
Empties the file
raw_input('prompt:')
Reads a line of input from user and returns as string
pop()
method removes and returns the last object from a list
boolean value
True or False
function
1. Names code like variables name strings/numbers 2. Takes arguments the way scripts take argv 3. Using 1 and 2, allows for mini-commands
""" ............."""
String for multiple lines of text; can be multi-line comment
floating point numbers
-Scientific notation in computers -Allows very large and small numbers using exponents -Made up of: Significand: 5, 1.5, -2.001 Exponent: 2, -2 -Put decimal after integers to make floating point 1 ~ 1.0
%s
String format character; use for user formatting
Treat if statements like...
..paragraphs. Each if, elif, and else grouping is like a set of sentences. Put blank lines before and after.
open()
- function opens a file - Required argument is filename - Default access_mode is read(r) - Does not return actual content; creates/reads fileObject -
append()
Adds input to the end of a list
Ordinal Numbers
Start at 1; First, second, third
Cardinal Numbers
Start at 0
len(input)
Return the number of items from a sequence or characters in a string
Never nest if-statements more than..
..two deep. Try to do one deep (put inside another function).
sorted()
Sorts a list from smallest to highest or a string alphabetically sorted(str, reverse=True) <- Sorts backwards
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
print to console
Boolean tests should be..
...simple. If complex, move calculations to variables earlier in function and use a good name for the variable.
input()
Assumes input is valid python expression, returns evaluated result
upper()
converts a string to uppercase
==
equal
write(stuff)
Writes stuff to file
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
lower()
converts a string to lowercase
\
escape; tells python to ignore following character, or puts difficult characters into strings when used with specific escape sequences
A while-loop is...
an infinite loop. "while True" ~ "While true is true, run this:"
x += y
ADD AND x = x + y
readline()
Reads one line of text file
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)
def
Defines a function def function1(): print "this is function 1"
int()
Convert a string to an integer int(raw_input(> ))
!=
not equal
A for-loop is...
lower()/upper()
convert input to upper or lowercase
Every if statement must have a(n)...
else
5 % 3
Modulo; remainder of the division 5 % 3 = 2 (3 goes into 5 once, remainder 2)
How many characters to a line?
80 characters
round()
function rounds floating point numbers round(1.773) = 2
line character; creates new line in string
close()
- method flushes unwritten information and closes file object - Not necessary, but important best practice
Section 2
(50 cards)
except
catches the exception and executes codes
%c
Single character -accepts integer or single char string
%o
unsigned octal
\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.
%i
signed integer decimal
%u
unsigned decimal
\\
backslash (\)
%g
Same as "e" if exponent is greater than -4 or less than precision
ASCII LineFeed (LF) - Goes to next line -newline escape
else
optional. Used after elif to catch other cases not provided for.
%f
Floating point decimal format (lowercase)
is
tests for object identity
or
at least one condition must be met
continue
used to interrupt the current cycle, without jumping out of the whole cycle. New cycle will begin.
%E
Floating point exponential format (uppercase)
and
all conditions in a boolean expression must be met
global
access variables defined outside functions
not
negates a boolean value
try
specifies exception handlers
%G
Same as "E" if exponent is greater than -4 or less than precision
%x
Unsigned hexadecimal (lowercase)
del
deletes objects
\a
ASCII Bell -may cause receiving device to emit a bell or warning of some kind
from
for importing a specific variable, class or a function from a module
\'
Single Quote (')
for
iterate over items of a collection in order they appear
yield
is used with generators
return
exits the function and returns a value
%d
signed integer decimal
exec
executes Python code dynamically
elif
stands for else if. if the first test evaluates to False, continues with the next one
%F
Floating point decimal format (UPPERCASE)
%X
Unsigned Hexadecimal (uppercase)
\"
Double-quote (")
pass
does nothing
class
-way of producing objects with similar attributes and methods. -used to create new user defined objects -an object is an instance of a class
as
if we want to give a module a different alias
finally
is always executed in the end. Used to clean up resources.
assert
used for debugging purposes
if
Used to determine, which statements are going to be executed
lambda
creates a new anonymous function
import
import other modules into a python script
break
interrupt the (loop) cycle
raise
create a user defined exception
\v
ASCII Vertical Tab (VT) - 6 vertical lines; 1 inch
%e
Floating point exponential format (lowercase)
def
used to create a new user defined function
\t
ASCII Horizontal Tab (TAB) - 8 horizontal spaces; tab
\b
ASCII Backspace (BS) - Erases last character printed
Section 3
(50 cards)
function argument
passed in for function parameter function(argument)
type()
returns argument value type; str, int, float, etc
function parameter
Variable name for passed in argment def function(parameter):
instance variable
variable only available to one instance of a class
sys
module - contains important objects and functions
os
module - OS routines for NT or POSIX
bit mask
variable used to determine if bits are on or off in an input -sort of works like a multiple choice test key -can be used with | to turn bits on if off -use with ^ and 11111111 to flip all bits def check_bit4(input): mask = 0b1000 desired = input & mask if desired > 0: return "on" return "off"
list slicing
Way to access elements list[start:end:stride] -stride = count by __'s -any term can be omitted, will be set to default - a negative stride progresses through list backwards
zip()
Combines two or 3 lists to return all values in for loops
items()
Returns a list of a dict's tuple pairs (key, value)
filter()
-filters a list for terms that make the function true filter(function, list) filter(lambda x: x%3 ==0, my_list) -for anonymous (throwaway) functions
~88
Bitwise NOT flips all bits in a number for integers, effectively adds 1 and makes negative
// (operator)
Floor Division. Numbers after the decimal in the quotient are removed - 9//2 = 4
member variables
variables only available to members of certain class
sort()
sorts a list from smallest to greatest
=
assigns values from right side operands to left side operand
<>
Value of two operands not equal? -Similar to !=
8 & 5
bitwise AND Turns on bits turned on in BOTH inputs 0b100 & 0b101 = 0b100
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 *
%r
String -converts any python object using repr()
%s
String -Converts any python object using str()
5 << 1
bitwise left shift -shifts turned on bits to the left 0b001 << 1 = 0b010
12 ^ 42
Bitwise XOR, EXCLUSIVE OR Turns bits on if EITHER but not BOTH bits of inputs are turned on 0b1010 ^ 0b1101 = 0b0111
Syntax to index 2 nested lists?
list[x][y]
abs()
returns absolute value
range()
Returns a list of numbers from start up to (but not including) stop start defaults to 0 and step defaults to 1 range(stop) range(start, stop) range(start, stop, step)
del keyword
deletes key/value pairs from dict
%=
Modulus AND. Takes modulus using two operands and assigns the result to left operand A%=B ~ A = A%B
-=
Subtract AND. Subtracts right operand from left and assigns the result to the left. A-=B ~ A = A - b
max()
returns maximum
values()
Returns an array of dict's values
9 | 4
Bitwise OR Turns on bits if turned on in either input 0b001 | 0b100 = 0b101
"mutable"
can be changed after created
method
function of an object
keys()
Returns an array of dict's keys
*=
Multiply AND. Multiplies left operand by right and assigns product to left operand A=B ~ A = AB
tuple
An immutable sequence of Python objects -Immutable; can't be changed -Similar to list, but can't be modified - Uses (), ends in ; tuple1 = ('word', 1, False);
list comprehension
Python rules for creating lists intelligently s = [x for x in range(1:51) if x%2 == 0] [2, 4, 6, 8, 10, 12, 14, 16, etc]
+=
Add AND. Adds right operand to the left and assigns the result to the left. A += B ~ A = A + B
min()
returns minimum
dictionary
A list whose objects can be accessed with a key instead of an index. Key can be any string or number. d = {'key1' : 1, 'key2' : 2}
items()
Returns an array of dict key/value pairs
**=
Exponent AND. Performs exponential calculation on operators and assigns value to left operand. A*=B ~ A = A*B
for loop
for variable in list_name: -variable is assigned each list item in turn -indented code below executed on each list item
%
no argument converted, results in "%" in the result
global variable
available everywhere
5 >> 4
bitwise right shift -shifts turned on bits to the right 0b010 >> 1 = 0b001
get()
Returns a value for the given key. If key is not available, returns default of 'none'.
enumerate()
gives an index number to each element in a list
.remove()
removes items from list
Section 4
(4 cards)