Comparisons & Conditionals

Comparisons & Conditionals#

Note: You can explore the associated workbook for this chapter in the cloud.

Writing Python code is a lot like writing a list of detailed instructions to the computer. Most of the time you will be asking the computer to perform certain tasks if certain conditions are met. For example:

If a person in the dataset is older than 30, then print out their name
If a tweet contains the phrase “ok boomer,” then automatically retweet it
If Beyoncé is a Grammy award-winner, then say “Congratulations, Beyoncé!

Here’s how we would write out this last example in Python code:

beyonce = "Grammy award-winner"

if beyonce == "Grammy award-winner":
    print("Congratulations, Beyonce!")

Congratulations, Beyonce!

There are two important Python elements present in the code above: a comparison and a conditional. We compared whether the variable beyonce is equal to the value "Grammy award-winner". Then we printed “Congratulations” if this condition was True.

Comparisons#

There are many ways that we can compare values with Python, such as equals (==), not equals (!=), greater than (>), less than (<), greater than or equal to (>=), or less than or equal to (<=).

Comparison Operator	Explanation
`x == y`	`True` if x is equal to y
`x != y`	`True` if x is not equal to y
`x > y`	`True` if x is greater than y
`x < y`	`True` if x is less than y
`x >= y`	`True` if x is greater than or equal to y
`x <= y`	`True` if x is less than or equal to y`

Greater Than#

Is the variable person1 greater than person1?

person1 = 30
person2 = 30.5
person1 > person2

Not Equals#

Is the variable person1 not equal to person1?

person1 = 30
person2 = 30.5
person1 != person2

We can also combine values and compare them. We can check to see if x and y are both True or if either x or y is True.

Logical Operator	Explanation
`x and y`	`True` if x and y are both True
`x or y`	`True` if either x or y is True
`not x`	`True` if is x is not True

And#

What will happen if we check whether person1 > 30 and person2 > 30?

person1 = 30
person2 = 30.5
person1 > 30 and person2 > 30

The boolean answer is False because person1 is not greater than 30 (person1 is exactly 30) even though person2 is greater than 30. The and requires that both conditions are True.

person1 = 30
person2 = 30.5
person1 >= 30 and person2 >= 30

True

The boolean answer is True because person1 is greater than or equal to 30 and person2 is greater or equal to 30. The and requires that both conditions are True.

Or#

What will happen if we check whether person1 > 30 or person2 > 30?

person1 = 30
person2 = 30.5
person1 > 30 or person2 > 30

The boolean answer is True because person2 is greater than 30. The or requires that only one of the conditions is true.

Conditionals#

If Statement#

An if statement is an instruction to do something if a particular condition is met.

A common conditional will consist of two lines:

On the first line, you type the English word if followed by an expression and then a colon (:)
On the second line, you indent and write an instruction or “statement” to be completed if the condition is met

beyonce = "Grammy award-winner"

if beyonce == "Grammy award-winner":
    print("Congratulations, Beyonce!")

Python is picky about how you format if statements. Look what happens if we forget to tab over on the second line or if we forget the colon:

if beyonce == "Grammy award-winner":
print("Congratulations, Beyonce!")

if beyonce == "Grammy award-winner"
    print("Congratulations, Beyonce!")

Else Statement#

You can add even more complexity in a conditional by adding an else statement. This will instruct the program to do something in case the condition is not met. An else comes after an if statement and should be formatted it the same way.

beyonce = "not a Grammy award-winner this year"

if beyonce == "Grammy award-winner":
    print("Congratulations, Beyonce!")
else:
    print("They messed up, Beyonce.")

Elif Statement#

Sometimes you want even more nuance to respond to slightly different conditions. For example, if Beyonce was nominated for a Grammy but didn’t win, then we might want to express a slightly different sentiment than if she won or was not nominated at all.

You can add in this nuance with an elif statement, short for else if. The computer will evaluate the first if statement. If that statement is not True, it will then evaluate the elif statement.

beyonce = "Grammy award-nominee"

if beyonce == "Grammy award-winner":
    print("Congratulations, Beyonce!")
elif beyonce == "Grammy award-nominee":
    print("Ok well at least they nominated you, Beyonce.")
else:
    print("They messed up, Beyonce.")

Excerises#

For the following exercises and the next few lessons, we’re going to draw on Anelise Shrout’s Bellevue Almshouse Dataset. The Bellevue Almshouse Dataset includes information about Irish-born immigrants who were admitted to the almshouse in the 1840s.

The Bellevue Almshouse was part of New York City’s public health system, a place where poor, sick, homeless, and otherwise marginalized people were sent — sometimes voluntarily and sometimes forcibly. Devastated by widespread famine in Ireland, many Irish people fled their homes for New York City in the 1840s, and many of them ended up in the Bellevue Almshouse. This dataset was transcribed from the almshouse’s own admissions records.

	date_in	first_name	last_name	age	disease	profession	gender	children
0	1847-04-17	Mary	Gallagher	28.0	recent emigrant	married	f	Child Alana 10 days
1	1847-04-08	John	Sanin (?)	19.0	recent emigrant	laborer	m	Catherine 2 mo
2	1847-04-17	Anthony	Clark	60.0	recent emigrant	laborer	m	Charles Riley afed 10 days
3	1847-04-08	Lawrence	Feeney	32.0	recent emigrant	laborer	m	Child
4	1847-04-13	Henry	Joyce	21.0	recent emigrant	NaN	m	Child 1 mo
5	1847-04-14	Bridget	Hart	20.0	recent emigrant	spinster	f	Child
6	1847-04-14	Mary	Green	40.0	recent emigrant	spinster	f	And child 2 months
7	1847-04-19	Daniel	Loftus	27.0	destitution	laborer	m	NaN
8	1847-04-10	James	Day	35.0	recent emigrant	laborer	m	NaN
9	1847-04-10	Margaret	Farrell	30.0	recent emigrant	widow	f	NaN
10	1847-04-10	Bridget	Day	30.0	recent emigrant	married	f	NaN
11	1847-04-10	Anthony	Day	0.5	recent emigrant	NaN	m	NaN
12	1847-04-07	James	Collins	22.0	recent emigrant	laborer	m	NaN
13	1847-04-07	Thomas	Collins	21.0	recent emigrant	laborer	m	NaN
14	1847-04-07	Pat	Whalen	25.0	recent emigrant	laborer	m	NaN
15	1847-04-17	Dan	Delany	10.0	typhus	NaN	m	NaN
16	1847-04-09	Catherine	O'Harra	23.0	recent emigrant	married	f	NaN
17	1847-04-09	Damiel	O'Harra	25.0	recent emigrant	laborer	m	NaN
18	1847-04-12	Margaret	Delaney	26.0	recent emigrant	married	f	NaN
19	1847-04-12	Michael	Delany	3.0	recent emigrant	NaN	m	NaN

We’re using the Bellevue Almshouse Dataset to practice if, elif, and else statements because we want to think deeply about the consequences of reducing human life to data and evaluating “Truth” in Pythonic terms even at this early stage in our Python journey.

As Shrout argues in her essay “(Re)Humanizing Data: Digitally Navigating the Bellevue Almshouse,” “Nineteenth-century immigration data was produced with the express purpose of reducing people to bodies; bodies to easily quantifiable aspects; and assigning value to those aspects which proved that the marginalized people to who they belonged were worth less than their elite counterparts.”

As you complete the exercises below, reflect about the categories that these Irish immigrants were slotted into by the government. For example, the so-called “disease” that many of the people in this dataset exhibited — the reason they were admitted to the Almshouse in the first place — is “recent emigrant.” What does this uncomfortable fact tell us about data more broadly? What should we make of the fact that Python, as a programming language, doesn’t understand the meaning or historical context of this data?

Exercise 1#

person1_name = 'Mary Gallagher'
person1_age = 28
person1_disease = 'recent emigrant'
person1_profession = 'married'
person1_gender = 'f'
person1_child_status = 'Child Alana 10 days'

Write an if statement that reports whether person1_age is less than 30 years old

#Your code here
    print('Person is less than 30 years old.')

Exercise 2#

Write an if statement that reports whether person1_profession is “married”

#Your code here
    print('Person is married.')

Person is married.

Exercise 3#

Write an if statement that reports whether person1_age is less than 30 years old and person1_profession is “married”

#Your code here
    print('Person is less than 30 years old and married.')

Person is less than 30 years old and married.

Exercise 4#

person2_name = 'Anthony Clark'
person2_age = 60
person2_disease = 'recent emigrant'
person2_profession = 'laborer'
person2_gender = 'm'
person2_child_status = 'Charles Riley afed 10 days'

Combine anif statement with an else statement that will report whether person2_age is less than 30 years old or, if not, more than 30 years old

#Your code here
    print('Person is less than 30 years old.')
#Your code here
    print('Person is more than 30 years old.')

Person is more than 30 years old.

Exercise 5#

person3_name = 'Margaret Farrell'
person3_age = 30
person3_disease = 'recent emigrant'
person3_profession = 'widow'
person3_gender = 'w'
person3_child_status = ''

Add an elif statement that reports whether person3_age is exactly 30 years old

#Your code here
    print('Person is less than 30 years old.')
#Your code here
    print('Person is exactly 30 years old.')
#Your code here
    print('Person is more than 30 years old.')

Person is exactly 30 years old.

Exercise 6#

person1_child_status = 'Child Alana 10 days'
person3_child_status = ''

Write an if statement that will report whether person1_child_status includes children

#Your code here
    print('Person has children.')

Person has children.

Exercise 7#

Write a single if statement that will accurately report whether person1_child_status includes children and if person3_child_status includes children

Hint

Think about how you might use the != operator!

And remember that there’s a difference between quotation marks with no space '' and quotation marks with a space' '. Python is picky!

if person1_child_status #Your Code Here
    print('Person has children.')

if person2_child_status #Same Code Here
    print('Person has children.')

Excerise 8#

person1_profession = 'married'

Write a conditional that will report whether person1_profession is “married,” “laborer,” “widow,” or “unknown profession.” Then test your code by reassigning the variable as indicated below.

#Your code here
    print('Person is married.')
#Your code here
    print('Person is a laborer.')
#Your code here
    print('Person is a widow.')
#Your code here
    print('Person has unknown profession.')

Person is married.

person1_profession = 'laborer'

#Your code here
    print('Person is married.')
#Your code here
    print('Person is a laborer.')
#Your code here
    print('Person is a widow.')
#Your code here
    print('Person has unknown profession.')

Person is a laborer.

person1_profession = 'student'

#Your code here
    print('Person is married.')
#Your code here
    print('Person is a laborer.')
#Your code here
    print('Person is a widow.')
#Your code here
    print('Person has unknown profession.')

Person has unknown profession.

Exercise 9#

person4_name = 'John Sanin(?)'

Some of the Irish immigrants’ names have question marks after them. Let’s clean up some of the data and remove the question marks.

You can use the Python keyword in to test whether a string appears within another string. Print person4_name with the question mark and parentheses removed.