week 2 variables Flashcards
variable
named storage spot (‘box’) that holds value assigned by three properties
three properties of a variable
name/identity, type, and value
int
single whole number, integer
real values/ floating
decimal (needs bigger ‘box’)
string
letter(s) “ “
boolean
true or false
type function
type()
determines type of variable, can be verified with print
i.e print(type(variable))
how many numbers can a variable store?
one, it can be altered through reassignment
defining strings
first = “Ada”
last = “Lovelace”
concatenating strings
full = first + last
full = “AdaLovelace”
-> no space
how do you add numbers to a string
convert num to string with str() function
len(char)
number of characters
user.lower()
lowercases all alphabets
indexing username[0]
returns first character, starts at 0
immutable
cant be changed, strings can’t be altered through indexing
username[7] = “i”
ERROR.
string slicing
lets you select sections of a string
my_str[0:9]
returns first 10 characters
my_str[10:-5]
does 5 indices after 10, including 10
so basically 10 11 12 13 14 15
my_str[8:]
everything after 8
my_str[:8]
everything before 8
my_str[:-1]
everything but last character
find(x)
returns the index of the first occurrence of string x
**
power sign
//
integer division, number without remainder
%
modulus, remainder
26 // 5
5
26 % 5
1
module
library in python that has list of functions
format()
used to format output specified in string before
print(“Total Cost: ${:.2f}”.format(cost))
formats the cost by adding a dollar sign and only including two numbers after the decimal point
incrementing
increasing a variable’s value by 1
identifiers
names used by a programmer for items, sequences of letters, numbers and underscore
a identifier must start with…
letter or underscore, and its case-sensitive
PEP 8
python enhancement proposal, which outlines the basics of python. it suggests identifiers should be lowercase with underscore between words
object
represents a value and is automatically created by the interpreter when executing a line of code
examples of objects
integers, strings, functions, lists, etc
temporary versus permanent objects
print(2+2) is temp
x = 7 is permenant
garbage collection
deleting unused objects to free memory space
name binding
associating names with interpreter object
properties of objects
value, type, and identity
immutable types
integers and strings, they can only be reassigned in new objects
id()
gives value of object identity
print(id(‘ABC’))
create and print identity of a string
floating point literal
written with fractional part even if its a whole number (like 0.0, 1.0, 9.0, etc)
scientific notation
representing super large or small numbers in terms of e
max floating point number
1.8e308
min floating point number
2.3e-208
overflow
when value is too large to be stored in memory allocated by interpreter
float should be used for…
measured values (ex: temperature)
int should be used for…
counted values (ex: students)
when specifying format, python ___ last digit
rounds
expression
combo of items like vars, literals, operators, and parenthesis, that evaluate to a value
ex: 2* (x + 1)
literal
specific value in code (ex: 2)
operator
symbol that preforms built-in calculation
precedence rules
ordered standard mathematics.
PEMDAS
() first
** second
- negative third
* / % mult, div, and % fourth
+ - add, sub, fifth
evaluate left to right for equal precedence
compound operators
shorthand to update variables
age += 1
age = age + 1
age -= 1
age = age - 1
age *= 1
age = age * 1
age /= 1
age = age / 1
age %= 1
age = age % 1
//
floor division, rounds down and returns integer
5.0 // 2
2.0
if operand is float, returns float
script
python program written in a file which is passed to python interpreter as input
import
statement that makes module available for use
ex:
import math
dot notation
used to access objects defined in module
if module is universe
and variable is speed…
universe.speed
when imported, ____ code in module executes
all
math module
standard python module that supports advances mathematics operations
function
list of statements that can be executed by referencing functions name
function call
process of invoking function
argument
item passed to a function
unicode
code that represents every possible character as a unique number
ASCII
code point
unique numbers in unicode
escape char \
single backslash
escape char '
single quote
escape char "
double quote
\t
tab/indent
raw string
ignores the escape sequences, created by adding r before string literal
ord()
returns encoded integer value for string of length 1
ex: ord(‘H’) returns 72
chr()
returns string of one char for encoded int
ex: chr(72) returns ‘H’
