4.4 KiB
Codecademy's Python 2 Course
https://www.codecademy.com/courses/learn-python/lessons/python-syntax/
It's gratis and accepts Python 3 syntax.
Object-oriented
"The main goal of an object oriented language is to make code reusable – we do this through the use of classes and objects. If we want to design a new type of car, we can start with what they all have in common: wheels, seats, a frame. Now that we’ve determined what cars have in common, we can more easily implement any type of car we want by starting from that basic blueprint."
https://discuss.codecademy.com/t/what-does-it-mean-that-python-is-an-object-oriented-language/297314
Errors (ex6, CH1, P3)
"SyntaxError means there is something wrong with the way your program is written — punctuation that does not belong, a command where it is not expected, or a missing parenthesis can all trigger a SyntaxError.
A NameError occurs when the Python interpreter sees a word it does not recognize. Code that contains something that looks like a variable but was never defined will throw a NameError."
SyntaxError example: SyntaxError: EOL while scanning string literal
Math (ex6)
mirthful_addition = 12381 + 91817
amazing_subtraction = 981 - 312
trippy_multiplication = 38 * 902
happy_division = 540 / 45
sassy_combinations = 129 * 1345 + 120 / 6 - 12
exponents = (16 ** 0.5) # 16 to the 1/2th power. (4)
remainder = (15 % 2) # The remainder (and thus the result) equals 1
Find the remainder of a number using %
is_this_number_odd = 15 % 2
is_this_number_divisible_by_seven = 133 % 7
Updating variables / operators.
sandwich_price += sales_tax
is the same as:
sandwich_price = sandwich_price + sales_tax
but is much shorter.
Comments
Are indicated by # or """This is not for running"""
Numbers
An integer is like 5, a float is a number with a decimal point like 5.0. They can also be in scientific notation like 2.3e7
In Python 2, you need to make sure math like 7/2 = 3.5 is correct is by inputting it into Python like 7./2. or float(7)/2
Limitations of floats
Floats are limited by the number of digits. For example 1/3 = 0.3
>>> format(math.pi, '.12g') # give 12 significant digits
'3.14159265359'
>>> format(math.pi, '.2f') # give 2 digits after the point
'3.14'
Strings
Multi-line strings are marked by
Mulit-
line
strings"""
Booleans (True/False)
True = int(1) False = int(0)
Datatypes
Force treating as a string: str(7) Force treating as an integer: int("7") Froce treating as a float: float(7)
Escaping Characters
Simply add a \ to escape a character that would otherwise cause issues.
Arrays / Indexes
cows = "cows"[0]
This sets the variable cows to the 0th letter of the string "cows" which is c. These indexes start at 0, not 1.
Strings
String Methods
len(var) Get length of string.
var.lower() Force lowercase
var.upper() Force uppercase
str(var) Force treating variable as a string.
If it uses dot notation like .lower(), it works exclusively on strings.
Concatenation
"Ten times a cow is equal to " + result + " with 10 times as many breeding opportunities."
or
print(var, var2, var3)
or
string1 += string2
String Formatting with %
"%s %s - 2020" % (month, day) # Replace %s with a variable. First the month, then the day.
Add %03d to specify a signed integer padded 2 places with zeros. For example, 2 becomes 02.
This is super useful for displaying dates like this: print("%02d-%02d-%02d") % (now.month, now.day, now.year) or time like this: print '%02d:%02d:%04d' % (now.hour, now.minute, now.second) (Ch3, Ex. 4)
Date and Time (Ch3)
Grab the current time:
from datetime import datetime
now = datetime.now()
year = now.year
month = now.month
day = now.day
Fun Projects
Design a shop using Ex7 and Ex9 as a frame:
7:
money_in_wallet = 40
sandwich_price = 7.50
sales_tax = .08 * sandwich_price
sandwich_price += sales_tax
money_in_wallet -= sandwich_price
9:
cucumbers = 1
price_per_cucumber = 3.25
total_cost = cucumbers * price_per_cucumber
print(total_cost)
total_price += nice_sweater
Cool concept from Ch2 Ex15:
name = raw_input("What is your name? ")
quest = raw_input("What is your quest? ")
color = raw_input("What is your favorite color? ")
print "Ah, so your name is %s, your quest is %s, " \
"and your favorite color is %s." % (name, quest, color)