Chapters 2-4: Functions and Conditionals Flashcards
Boolean Expression
Expression either true or false.
=
Assignment operator
==
Comparison operator - equals
greater than, =/greater than, is/is not operators
> , >=, is, is not
elif
Used after the if, short for else if. can be as many as you want in a block, or none. Used same as if, ie if …..:
else
used at and of the block (if needed) - sets what happens if no conditions (if and elif) are met). used by itself, ie else:
nested conditional
when a conditional eg ‘else:’ has 2 sub braches, eg an if and an else
try/except
try: some code. if there is an error (eg cant float an input because it’s words), move on to the except:. No exception? skip the except:.
Guardian pattern
A logical expression guarding against a runtime error, using the fact logical expressions are evaluated left to right. eg [something] and x!=0 and (3/x)>2. x!=0 guards against runtime error caused if x=0, as 3 cant be divided by it.
what error message tells you about error locaction
tells you where python detected the error, not necessarily where it is. true error may be earlier in code.
Function
named sequence of statements that performs a computation, eg type()
Argument
the expression in the brackets of a function, ie the the expression the function “takes” before it “return”s a “value”
max()/min()
Functions which return the largest/smallest character/number in a string/comma’d list
len()
Function which returns the number of characters in a string
import math
Imports the “math” module. Can then be used, eg assign radians=0.7, height=math.sin(radians) (prefix functions with math.)
import random
Imports the “random” module, allows the generation of pseudorandom (deterministic but you cant really tell) with various random.functions
x=random.random()
Assigns x as random number between 0.0 and 1.0 (inclusive of 0.0 but not 1.0)
random.randint(1, 10)
Returns a pseudorandom number between 1 and 10 inclusive.
x=[1, 3, 5, 7]
Assigns x as a sequence, from which individual numbers can be chosen.
random.choice(x)
Returns a pseudorandom choice from a pre-assigned sequence, x.
def
defines a function, eg def print_lyrics(): // [tab]print(‘xxxxx’). 1st line is head, ends with “:”. Rest is the body, indented.
def x(y)
z(y)
z(y)
defines a function with (a) parameter(s). Python learns to do the same regardless of parameter if the y is the same in x(y) and z(y)
fruitful vs void function
function which returns a ‘worked-out’ result eg input() or math.sqrt(), vs a function which performs a task eg print()
return
used in the body of a function definition, to return the result of a fruitful function, eg def addtwo(a, b)//[tab]added=a+b//[tab]return added. Without final line, python adds the parameters but the result isnt reported, so it’s pointless.
None
A type of value, just like str or int, which means it is the result of a void function, or a fruitful function where the output has not been returned.
round(x, n)
Function, rouund a number, x, to n decimal places.
quit()
quit python/python environment
user_input=input(‘Type something!\n’)
assigns user_input variable with the vavlue user enters
Semantic error
The situation in which a program executes but does not produce the results that were intended. No error message, just wrong result.
Syntactic error
Error on syntax, ie grammar, of the command which means the interpreter cannot intrpret it. Leads to error message.
Logic error
An error in logic, often due to order of statements being wrong, or how the relate to one another.
Variable
A name you can assign a value, e.g. a=45, message=’hey man’. ‘x’ not needed for variables, but is for value. Python interprets these IDENTICALLY to their value unless changing the value with variable=something new. Case sensitive!
int()/float()/str()
returns argument as given type. convert with x=int(‘x’) etc
**
exponentiation, eg 5**2 = 5^2 = 25. alongside
//
/ but truncates result to an interger, i.e. rounds down to nearest interger. 5.9//2=2.0
%
modulus, gives the remainder not the quotient. 7//3=2, 7%3=1. v. useful, used in clever ways.
