My notes and maybe some exercises to follow along with the e-book "Learn Python the Hard Way" by Zed Shaw. Added here for 100 Days of Code.
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@(WWC - Learn Python the Hard Way)
###Exercise 0 - Setup
- Author does NOT recommend setting up IDLE
- Author does NOT recommend Python 3.0
- Instruction for setting up Python on Windows and Mac and Linux are extensive
- Author offers tips for finding answers to coding questions on Google
- Some tips for navigating directories from inside a terminal
###Exercise 1 - A Good First Program
file ex1.py contains:
print "Hello World!"
print "Hello Again"
print "I like typing this."
print "This is fun."
print 'Yay! Printing.'
print "I'd much rather you 'not'."
print 'I "said" do not touch this.'
run this script by typing this in the terminal:
python ex1.py
This exercises focuses on showing the relationship between the text editor and the terminal - what is typed in the file and what comes out at the end.
:# is called "octothorpe" for some reason
###Exercise 2 - Comments and Pound Characters
Comments are important to all programs for:
- purposes of documenting what we're doing in the program, as explanation and as way-points
- debugging so coder can eliminate lines to find the source of a problem
ex2.py is:
# A comment, this is so you can read your program later.
# Anything after the # is ignored by python.
print "I could have code like this." # and the comment after is ignored
# You can also use a comment to "disable" or comment out a piece of code:
# print "This won't run."
print "This will run."
In this chapter, the author recommends a debugging technique - read the code backwards. I've done this and it's especially helpful when you've been looking at the same lines for a while and getting nothing new out of them. Reading them backwards helps by forcing your brain to focus on little parts at a time, rather than skimming the whole.
###Exercise 3 - Numbers and Math
Math and math symbols:
+ plus
- minus
/ slash
* asterisk
% percent
< less-than
> greater-than
<= less-than-equal
>= greater-than-equal
ex3.py:
print "I will now count my chickens:"
print "Hens", 25 + 30 / 6
print "Roosters", 100 - 25 * 3 % 4
print "Now I will count the eggs:"
print 3 + 2 + 1 - 5 + 4 % 2 - 1 / 4 + 6
print "Is it true that 3 + 2 < 5 - 7?"
print 3 + 2 < 5 - 7
print "What is 3 + 2?", 3 + 2
print "What is 5 - 7?", 5 - 7
print "Oh, that's why it's False."
print "How about some more."
print "Is it greater?", 5 > -2
print "Is it greater or equal?", 5 >= -2
print "Is it less or equal?", 5 <= -2
The script does not produce fractions, despite the division above because int is the default type when doing some math without variables.
Division in this way rounds down the result (rather than return a fraction).
To get the math to work out correctly, it's necessary to assign the math to variables of type float
Floating types are assigned automatically when a variable is given a number with a decimal.
In this context, the % is called "modulus" and not percent - it does not calculate the percent of a number, it returns the remainder of a division operation.
Order of operations in Python is the same as in normal math. Acronym "PEDMAS" which stands for:
- parenthesis
- exponents
- multiplication
- division
- addition
- subtraction
###Exercise 4 - Variables and Names
Variables as defined in Python are pretty much the same as other programming languages EXCEPT variable names in Python must start with either an underscore or a letter.
No other punctuation is allowed.
Numbers are okay.
Uppercase is okay, but convention says "no".
Reminders of some debugging techniques learned so far:
- write comments above lines to describe what it's doing
- read the code backwards
- read the file out loud
My personal debugging notes:
- console log everything
- explain in great detail to someone else what the code is meant to do (rubber duck on a monitor)
ex4.py
cars = 100
space_in_a_car = 4.0
drivers = 30
passengers = 90
cars_not_driven = cars - drivers
cars_driven = drivers
carpool_capacity = cars_driven * space_in_a_car
average_passengers_per_car = passengers / cars_driven
print "There are", cars, "cars available."
print "There are only", drivers, "drivers available."
print "There will be", cars_not_driven, "empty cars today."
print "We can transport", carpool_capacity, "people today."
print "We have", passengers, "to carpool today."
print "We need to put about", average_passengers_per_car, "in each car."
FUN FACT: python will run as a calculator - type "python" into the terminal without providing the argument file name, and then just setup statements to be calculated.
= versus == is what? Single equal is an assignment, double equal is a comparison.
###Exercise 5 - More Variables and Printing
Strings. Another type, it exists between quotation marks.
ex5.py
my_name = 'Zed A. Shaw'
my_age = 35 # not a lie
my_height = 74 # inches
my_weight = 180 # lbs
my_eyes = 'Blue'
my_teeth = 'White'
my_hair = 'Brown'
print "Let's talk about %s." % my_name
print "He's %d inches tall." % my_height
print "He's %d pounds heavy." % my_weight
print "Actually that's not too heavy."
print "He's got %s eyes and %s hair." % (my_eyes, my_hair)
print "His teeth are usually %s depending on the coffee." % my_teeth
print "If I add %d, %d, and %d I get %d." % (
my_age, my_height, my_weight, my_age + my_height + my_weight)
%s and %r and %d are formatters - these stand in strings as placeholders for variables, listed at the end of the string. The variables listed at the end of the string will replace each formatter in the order they are listed.
Floating point numbers can be rounded with the built-in function round()
###Exercise 6 - Strings and Text
Strings are usually for display, always wrapped in single quotes or double quotes.
ex6.py
x = "There are %d types of people." % 10
binary = "binary"
do_not = "don't"
y = "Those who know %s and those who %s." % (binary, do_not)
print x
print y
print "I said: %r." % x
print "I also said: '%s'." % y
hilarious = False
joke_evaluation = "Isn't that joke so funny?! %r"
print joke_evaluation % hilarious
w = "This is the left side of..."
e = "a string with a right side."
print w + e
String concatenation with +
String formatter %r is for "raw" and for debugging (displays raw data of the variable) - the other formatters %s and %d are for displaying to users.
###Exercise 7 - More Printing
ex7.py
print "Mary had a little lamb."
print "Its fleece was white as %s." % 'snow'
print "And everywhere that Mary went."
print "." * 10 # what'd that do?
end1 = "C"
end2 = "h"
end3 = "e"
end4 = "e"
end5 = "s"
end6 = "e"
end7 = "B"
end8 = "u"
end9 = "r"
end10 = "g"
end11 = "e"
end12 = "r"
# watch that comma at the end. try removing it to see what happens
print end1 + end2 + end3 + end4 + end5 + end6,
print end7 + end8 + end9 + end10 + end11 + end12
Python style is 80 characters per line.
Print the character and * 10 repeats the character that many time - this saves a for/loop
###Exercise 8 - Printing, Printing
ex8.py
formatter = "%r %r %r %r"
print formatter % (1, 2, 3, 4)
print formatter % ("one", "two", "three", "four")
print formatter % (True, False, False, True)
print formatter % (formatter, formatter, formatter, formatter)
print formatter % (
"I had this thing.",
"That you could type up right.",
"But it didn't sing.",
"So I said goodnight."
)
Demonstrates the ways to combine strings with formatters. Note the use of the formatter variable used two ways. Output looks like this:
1 2 3 4
'one' 'two' 'three' 'four'
True False False True
'%r %r %r %r' '%r %r %r %r' '%r %r %r %r' '%r %r %r %r'
'I had this thing.' 'That you could type up right.' "But it didn't sing." 'So I said goodnight.'
%r may return (when string) the string in either single quote or double quote depending which is more efficient at the time. <--- this really sounds dubious, but it's almost a direct quote.
###Exercise 9 - Printing, Printing, Printing
ex9.py
# Here's some new strange stuff, remember type it exactly.
days = "Mon Tue Wed Thu Fri Sat Sun"
months = "Jan\nFeb\nMar\nApr\nMay\nJun\nJul\nAug"
print "Here are the days: ", days
print "Here are the months: ", months
print """
There's something going on here.
With the three double-quotes.
We'll be able to type as much as we like.
Even 4 lines if we want, or 5, or 6.
"""
This introduces the new line character \n
This introduces the triple quote use for blocks of text (string).
New line character does not work well with the %r formatter, which prints things in "raw" format, so the output is just "\n" rather than a new line.
###Exercise 10 - What Was That?
The backwards slash, back slash, \ is called an escape character and is used in various "escape sequences" to indicate to Python "the next character has special meaning"
Example of the need for this is to escape the single or double quote inside a string, as "it's" or 'Hello, "friend" of mine' - these should be written "it's" and 'Hello, "friend" of mine'
Example from the book:
"I am 6'2\" tall." # escape double-quote inside string
'I am 6\'2" tall.' # escape single-quote inside string
ex10.py
tabby_cat = "\tI'm tabbed in."
persian_cat = "I'm split\non a line."
backslash_cat = "I'm \\ a \\ cat."
fat_cat = """
I'll do a list:
\t* Cat food
\t* Fishies
\t* Catnip\n\t* Grass
"""
print tabby_cat
print persian_cat
print backslash_cat
print fat_cat
Escape sequences - this is a table copied directly from the book here: https://learnpythonthehardway.org/book/ex10.html
Escape What it does. \ | Backslash () ' | Single-quote (') " | Double-quote (") \a | ASCII bell (BEL) \b | ASCII backspace (BS) \f | ASCII formfeed (FF) \n | ASCII linefeed (LF) \N{name} | Character named name in the Unicode database (Unicode only) \r | Carriage Return (CR) \t | Horizontal Tab (TAB) \uxxxx | Character with 16-bit hex value xxxx (u'' string only) \Uxxxxxxxx | Character with 32-bit hex value xxxxxxxx (u'' string only) \v | ASCII vertical tab (VT) \ooo | Character with octal value ooo \xhh | Character with hex value hh
Author suggests putting each of these on a flash card to help memorize, but I'm using Anki for this instead.