Announcement

Tutoring and TA-ing Schedules

• Marcie Hogan (Tutor):
  1. Sunday, 2:00 PM--5:00 PM
  2. Wednesday, 12:30 PM--1:30 PM

• Andrew Mosbo (Tutor):
  1. Mondays, 4:00 PM--5:00 PM
  2. Wednesdays, 11:00 A.M.--noon
  3. Thursdays, 5:00 PM--6:00 PM

• Emine Morris (TA):
  1. Mondays and Wednesdays, 5:00 PM--6:30 PM
  2. Tuesdays and Thursdays, 3:00 PM--4:45 PM

Workflow

Shortcuts

• F9 runs a current line (where the blinking cursor bar is) or selected lines.

• Home/End moves the blinking cursor bar to the beginning/end of the line.

  • Fn + / works too.

• PgUp/PgDn moves the blinking cursor bar to the top/bottom line of the script on the screen.

  • Fn + / works too.

Workflow

Shortcuts

• # %% defines a coding block in Spyder IDE.

Workflow

More Shortcuts

• Ctrl (command for Mac Users) + Z undoes the previous action.
• Ctrl (command for Mac Users) + Shift + Z redoes when undo is executed.

• Ctrl (command for Mac Users) + F is useful when finding a phrase in the script.
• Ctrl (command for Mac Users) + R is useful when replacing a specific phrase with something in the script.

• Ctrl (command for Mac Users) + D deletes a current line.

Choose with if

if-else statement

• The if and else lines are Python statements that check whether a condition is a boolean True value, or can be evaluated as True.

disaster = True
if disaster:
    print("Woe!")
else:
    print("Whee!")Copy Code

• The recommended style is to use four spaces before the statement below if/else.

Choose with if

Compare with if, elif, and else

If there are more than two possibilities to test, use if for the first, elif (meaning else if) for the middle ones, and else for the last:

color = "mauve"
if color == "red":
    print("It's a rasberry")
elif color == "green":
    print("It's a green chili")
elif color == "bee purple":
    print("I don't know what it is, but only bees can see it")
else:
    print("I've never heard of the color", color)Copy Code

Choose with if

Compare with if, elif, and else

• Indentation determines how the if and else sections are paired.

furry = True
large = True
if furry:
    if large:
        print("It's a yeti.")
    else:
        print("It's a cat!")
else:
    if large:
        print("It's a whale!")
    else:
        print("It's a human. Or a hairless cat.")Copy Code

Choose with if

Comparison Operators

• Here are Python's comparison operators:

Choose with if

Comparison Operators

• Here are Python's comparison operators:

# Assign x to 7
x = 7
x == 5    # Test equality
x == 7
5 < x
x < 10Copy Code

Choose with if

Boolean Operator

• The shaded regions show which parts each Boolean operator (and, or, not) selects.

Choose with if

Comparison Operators

• Logical operators have lower precedence than the chunks of code that they’re comparing.

  • This means that the chunks are calculated first, and then compared.

5 < x and x < 10Copy Code

• The easiest way to avoid confusion about precedence is to add parentheses:

(5 < x) and (x < 10)Copy Code

Choose with if

Comparison Operators

• Here are some other tests:

5 < x or x < 10
5 < x and x > 10
5 < x and not x > 10Copy Code

• If you’re and-ing multiple comparisons with one variable, Python lets you do this:

5 < x < 10      # It’s the same as 5 < x and x < 10Copy Code

Choose with if

What Is True?

• What does Python consider True and False?

• A False value doesn’t necessarily need to explicitly be a boolean False.
  • The followings are all considered False:

• Anything else is considered True.

Choose with if

What Is True?

• Python programs use these definitions of "truthiness" and "falsiness" to check for empty data structures as well as False conditions:

some_list = []
if some_list:
    print("There's something in here")
else:
    print("Hey, it's empty!")Copy Code

Choose with if

Do Multiple Comparisons with in

• Suppose that you have a letter and want to know whether it’s a vowel.
  • One way would be to write a long if statement:

letter = 'o'
if letter == 'a' or letter == 'e' or letter == 'i' \
    or letter == 'o' or letter == 'u':
    print(letter, 'is a vowel')
else:
    print(letter, 'is not a vowel')Copy Code

Choose with if

Do Multiple Comparisons with in

• Whenever you need to make a lot of comparisons like that, separated by or, use Python’s membership operator in, instead.

vowels = 'aeiou'
letter = 'o'
letter in vowels
if letter in vowels:
    print(letter, 'is a vowel')Copy Code

Choose with if

Do Multiple Comparisons with in

• Here are some examples of how to use in with some data types:

letter = 'o'
vowel_set = {'a', 'e', 'i', 'o', 'u'}
letter in vowel_setCopy Code

vowel_list = ['a', 'e', 'i', 'o', 'u']
letter in vowel_listCopy Code

vowel_tuple = ('a', 'e', 'i', 'o', 'u')
letter in vowel_tupleCopy Code

vowel_dict = {'a': 'apple', 'e': 'elephant',
              'i': 'impala', 'o': 'ocelot', 
              'u': 'unicorn'}
letter in vowel_dictCopy Code

vowel_string = "aeiou"
letter in vowel_stringCopy Code

Choose with if

Walrus Operator

• The walrus operator looks like this:

tweet_limit = 280
tweet_string = "Blah" * 50
diff = tweet_limit - len(tweet_string)
if diff >= 0:
    print("A fitting tweet")
else:
    print("Went over by", abs(diff))Copy Code

tweet_limit = 280
tweet_string = "Blah" * 50
if ( diff := tweet_limit - len(tweet_string) ) >= 0:
    print("A fitting tweet")
else:
    print("Went over by", abs(diff))Copy Code

Choose with if

Class Exercises

1. Choose a number between 1 and 10 and assign it to the variable secret. Then, select another number between 1 and 10 and assign it to the variable guess. Next, write the conditional tests (if, else, and elif) to print the string 'too low' if guess is less than secret, 'too high' if greater than secret, and 'just right' if equal to secret.

2. Assign True or False to the variables small and green, respectively. Write some if/else statements to print which of these matches those choices: cherry, pea, watermelon, pumpkin.

Text Strings

• Data scientists often work with strings of text.

• Strings in Python are immutable.

  • We can’t change a string in place, but we can copy parts of strings to another string to get the same effect.

Text Strings

Create with Quotes

• We make a Python string by enclosing characters in matching single or double quotes:

'Business'
"Data"Copy Code

• The Console (interactive interpreter) echoes strings with a single quote, but all are treated exactly the same by Python.

Text Strings

Create with Quotes

• Why have two kinds of quote characters?
  • The main purpose is to create strings containing quote characters.
  • We can have single quotes inside double-quoted strings, or double quotes inside single-quoted strings.

"'Nay!' said the naysayer. 'Neigh?' said the horse."
'The rare double quote in captivity: ".'
'A "two by four" is actually 1 1⁄2" × 3 1⁄2".'
"'There's the man that shot my paw!' cried the limping hound."Copy Code

Text Strings

Create with Quotes

• We can also use three single quotes (''') or three double quotes ("""):

'''Hi!'''
"""Hello!"""Copy Code

• The most common use of triple quotes is to create multiline strings:

poem_bluebird = '''there’s a bluebird in my heart that
wants to get out
but I’m too tough for him,
I say, stay in there, I’m not going
to let anybody see
you.'''Copy Code

Text Strings

Create with Quotes

• There’s a difference between the output of print() and the automatic echoing done by the interactive interpreter:

poem_bluebird
print(poem_bluebird)
print('Give', "us", '''some''', """space""")Copy Code

• print() strips quotes from strings and prints their contents. - It’s meant for human output.

Text Strings

Create with str()

• We can make a string from another data type by using the str() function:

str(3.141592)
str(1.0e4)
str(True)Copy Code

Text Strings

Escape with \

• Python lets us escape the meaning of some characters within strings to achieve effects that would otherwise be difficult to express.

  • By preceding a character with a backslash (\), we give it a special meaning.

• The most common escape sequence is \n, which means to begin a new line.

  • With this we can create multiline strings from a one-line string:

palindrome = 'A man,\nA plan,\nA canal:\nPanama.'
print(palindrome)Copy Code

Text Strings

Escape with \

print('\tabc')
print('a\tbc')
print('ab\tc')
print('abc\t')Copy Code

testimony = "\"I did nothing!\" he said. \"Or that other thing.\""
testimony
print(testimony)Copy Code

speech = 'The backslash (\\) bends over backwards to please you.'
print(speech)Copy Code

info = r'Type a \n to get a new line in a normal string'
infoCopy Code

poem = r'''Boys and girls, come out to play.
The moon doth shine as bright as day.'''
poem
print(poem)Copy Code

Text Strings

Combine by Using +

• We can combine literal strings or string variables in Python by using the + operator:

'DANL 100: Programming for ' + 'Data Analytics'Copy Code

• We can also combine literal strings (not string variables) just by having one after the other:

'DANL 100: Programming for ' 'Data Analytics'Copy Code

Text Strings

Duplicate with *

• We use the * operator to duplicate a string.

start = 'Na ' * 4 + '\n'
middle = 'Hey ' * 3 + '\n'
end = 'Goodbye.'
print(start + start + middle + end)Copy Code

Text Strings

Get a Character with []

• To get a single character from a string, specify its offset inside square brackets after the string’s name.

  • The first (leftmost) offset is 0, the next is 1, and so on.
  • The last (rightmost) offset can be specified with –1, so you don’t have to count; going to the left are –2, –3, and so on:

letters = 'abcdefghijklmnopqrstuvwxyz'
letters[0]
letters[1]
letters[-1]
letters[5]
letters[100]Copy Code

Text Strings

Get a Character with []

• Because strings are immutable, we can’t insert a character directly into one or change the character at a specific index.

name = 'Macintosh'
name[0] = 'P'Copy Code

• Instead, we need to use some combination of string functions such as replace() or a slice (which we look at in a moment):

name = 'Macintosh'
name.replace('M', 'P')
'P' + name[1:]Copy Code

Text Strings

Get a Substring with a Slice

• We can extract a substring (a part of a string) from a string by using a slice.

• We define a slice by using square brackets ([]), a start offset, an end offset, and an optional step count between them.

  • We can omit some of these.

• The slice will include characters from offset start to one before end:

Text Strings

Get a Substring with a Slice

letters = 'abcdefghijklmnopqrstuvwxyz'
letters[:]Copy Code

letters = 'abcdefghijklmnopqrstuvwxyz'
letters[20:]
letters[10:]
letters[-3:]
letters[-50:]Copy Code

letters = 'abcdefghijklmnopqrstuvwxyz'
letters[:3]
letters[:-3]
letters[:70]Copy Code

letters = 'abcdefghijklmnopqrstuvwxyz'
letters[12:15]
letters[-51:-50]
letters[70:71]Copy Code

letters = 'abcdefghijklmnopqrstuvwxyz'
letters[4:20:3]   # From offset 4 to 20, by steps of 3 characters
letters[::7]      # From the start to the end, in steps of 7 characters
letters[19::4]    # From offset 19 to the end, by 4
letters[:21:5]    # From the start to offset 20 by 5:
letters[-1::-1]   # Starts at the end and ends at the start
letters[::-1]Copy Code

• Offsets go 0, 1, and so on from the start to the right.
• Offsets go –1,–2, and so forth from the end to the left.

Text Strings

String-related Functions

len(letters)
empty = ""
len(empty)Copy Code

tasks = 'get gloves,get mask,give cat vitamins,call ambulance'
tasks.split(',')
tasks.split()Copy Code

crypto_list = ['Yeti', 'Bigfoot', 'Loch Ness Monster']
crypto_string = ', '.join(crypto_list)
print('Found and signing book deals:', crypto_string)Copy Code

setup = "a duck goes into a bar..."
setup.replace('duck', 'marmoset')
setup
setup.replace('a ', 'a famous ', 100) # Change up to 100 of them
setup.replace('a', 'a famous', 100) # If we're unsure the exact substringCopy Code

world = " earth "
world.strip()
world.lstrip()
world.rstrip()Copy Code

world = " earth "
world.strip(' ')
world.strip('!')
blurt = "What the...!!?"
blurt.strip('.?!')Copy Code

poem = '''All that doth flow we cannot liquid name
Or else would fire and water be the same;
But that is liquid which is moist and wet
Fire that property can never get.
Then 'tis not cold that doth the fire put out
But 'tis the wet that makes it die, no doubt.'''
word = 'the'
poem.count(word)Copy Code

Text Strings

Case and Allignment

• We have more built-in functions for case and allignment:

setup = 'a duck goes into a bar...'
setup.capitalize()    # Capitalize the first word
setup.title()    # Capitalize all the words
setup.upper()    # Convert all characters to uppercase
setup.lower()    # Convert all characters to lowercase
setup.swapcase()    # Swap uppercase and lowercase
setup.center(30)    # Center the string within 30 spaces
setup.ljust(30)    # Left justify
setup.rjust(30)    # Right justifyCopy Code

Text Strings

Formatting

• We’ve seen that we can concatenate strings by using +.

• Let’s look at how to interpolate data values into strings using f-strings formats.

  • f-strings appeared in Python 3.6, and are now the recommended way of formatting strings.

  • There exists an old style of string formatting with % and a new style of it with {}, which we may not discuss here.

Text Strings

Formatting

• To make an f-string:

  • Type the letter f or F directly before the initial quote.
  • Include variable names or expressions within curly brackets ({}) to get their values into the string.

thing = 'wereduck'
place = 'werepond'
f'The {thing} is in the {place}'
f'The {thing.capitalize()} is in the {place.rjust(20)}'Copy Code