It looks like we’re steering the computer in one of three possible directions:
if avg >= n[0]:
cityavgs[city_name] = "Everyone seems to want to live in "+city_name+" as prices are on the rise."
elif avg < n[0]:
cityavgs[city_name] = "Prices are low in "+city_name+". Is it a good deal? Or will it be the next Detroit?"
else:
cityavgs[city_name] = None
Lines
49–50
will never be executed,
so we can delete them:
if avg >= n[0]:
cityavgs[city_name] = "Everyone seems to want to live in " + city_name + " as prices are on the rise."
elif avg < n[0]:
cityavgs[city_name] = "Prices are low in " + city_name + ". Is it a good deal? Or will it be the next Detroit?"
The comparison in
line
47
is always true, so we can delete it:
if avg >= n[0]:
cityavgs[city_name] = "Everyone seems to want to live in " + city_name + " as prices are on the rise."
else:
cityavgs[city_name] = "Prices are low in " + city_name + ". Is it a good deal? Or will it be the next Detroit?"
Don’t write line longer than 80 characters:
if avg >= n[0]:
cityavgs[city_name] = "Everyone seems to want to live in " + city_name \
+ " as prices are on the rise."
else:
cityavgs[city_name] = "Prices are low in " + city_name \
+ ". Is it a good deal? Or will it be the next Detroit?"
In-depth study: the
if the user selects the city of
Cayce, South Carolina, the URL will download
this
JSON file.
In
line
39,
Data
is the
list
of 16 items created in lines
17
and
33;
Data[i]
is a
dictionary
with a key named
dataset (see the
JSON file);
Data[i]['dataset']
is a
dictionary
with a key named
data;
Data[i]['dataset']['data']
is a
list.
Each item on the list is a short list containing a date and a price.
That’s what the
d
and
p
in
line
40
stand for.
The
n[0]
in lines
45
and
47
is the first item in the
list
n
created in lines
38
and
41.
But the script uses only the first item on this list.
Making the rest of the list is therefore a waste of time.
Futhermore,
whenever we use
n[0]
(which happens only in lines
45
and
47),
the value of
n[0]
is always equal to the value of
Data[i]['dataset']['data'][0][1].
(Remember that
Data[i]['dataset']['data'][0][0]
is a date, and
Data[i]['dataset']['data'][0][1]
is a price.
They’re the date and price of the first sale in the
list
Data[i]['dataset']['data'].)
The following changes will therefore simplify the program
without changing its output at all,
and make it run faster.
n[0]
to
Data[i]['dataset']['data'][0][1].
n.
In
line
38,
remove the
n = []
and the preceding semicolon.
Remove
line
41.
if guess == secretNumber:
print("You got it! My number was {}.".format(secretNumber))
break
if guess in guesses:
print("You already guessed that number!")
# gives users a hint.
elif guess < secretNumber:
print("My number is higher than {}.".format(guess))
elif guess > secretNumber:
print("My number is lower than {}.".format(guess))
else:
print("That's not it!")
Lines 36–38 can never be executed, so we can remove them from the script without changing the behavior of the script.
if guess == secretNumber:
print("You got it! My number was {}.".format(secretNumber))
break
if guess in guesses:
print("You already guessed that number!")
# gives users a hint.
elif guess < secretNumber:
print("My number is higher than {}.".format(guess))
elif guess > secretNumber:
print("My number is lower than {}.".format(guess))
guess
is always greater than
secretNumber
whenever we arrive at
line
34,
so we can simplify
line
34
to the single word
else:
without changing the behavior of the script.
if guess == secretNumber:
print("You got it! My number was {}.".format(secretNumber))
break
if guess in guesses:
print("You already guessed that number!")
# gives users a hint.
elif guess < secretNumber:
print("My number is higher than {}.".format(guess))
else:
print("My number is lower than {}.".format(guess))
The four
print
statements
are mutually exclusive:
exactly one of them should be executed.
The notation that everybody expects you to use for four mutually exclusive
statements is
if/elif/elif/else.
I think it would be clearest if the
<,
>,
===
cases were consecutive.
if guess in guesses:
print("You already guessed that number!")
elif guess < secretNumber: #Give users a hint.
print("My number is higher than {}.".format(guess))
elif gess > secretNumber:
print("My number is lower than {}.".format(guess))
else:
print("You got it! My number was {}.".format(secretNumber))
break
Here’s the very interesting output:
ADMIN HEARNG Minimum annual salary: 40392 Maximum annual salary: 156420 ANIMAL CONTRL Minimum annual salary: 39528 Maximum annual salary: 130008 AVIATION Minimum annual salary: 45696 Maximum annual salary: 300000 etc. TRANSPORTN Minimum annual salary: 36840 Maximum annual salary: 169500 TREASURER Minimum annual salary: 46356 Maximum annual salary: 137700 WATER MGMNT Minimum annual salary: 43632 Maximum annual salary: 169512
Here’s the JSON file.
In
line
38,
dictionary
is a
dictionary
holding the entire
JSON
file;
dictionary["data"]
is a
list
of people.
(The script therefore would be easier to read if the variable
data
in
Line
38
had been named
person
or
employee.)
Each of these people is list is a list of 17 items.
Item number 10 (i.e., the item whose index is 10)
is the name of their department;
item number 17 is their salary.
Line
36
begins to create a
dictionary.
Each key in this dictionary is the name of a department.
The corresponding value is a
list
of two numbers,
the minimum amd maximum salary for that department.
Lines
43–46
check if each incoming person sets a new record for lowest or highest salary.
Before these lines can do that, however,
lines
39–40
have to make sure that the department,
with its minimum and maximum known salaries,
is already in the dictionary
dept.
On Thursday, August 27,
we saw in class how to eliminate the need
for
lines
39–40
by using the
collections.defaultdict
in
Popular.
That lets us change
lines
36–48
from
dept = {}
for data in dictionary["data"]:
if data[10] not in dept and data[14]!=None:
dept[data[10]] = [data[14], data[14]]
else:
try:
if float(data[14]) < float(dept[data[10]][0]):
dept[data[10]][0] = data[14]
if float(data[14]) > float(dept[data[10]][1]):
dept[data[10]][1] = data[14]
except TypeError:
continue
to the following.
Note that the salaries have decimal points,
so they’re
floats.
import collections
def defaultValue():
return [1000000000.00, 0.00] #minimum salary, maximum salary
dept = collections.defaultdict(defaultValue)
for data in dictionary["data"]:
try:
if float(data[14]) < float(dept[data[10]][0]):
dept[data[10]][0] = data[14]
if float(data[14]) > float(dept[data[10]][1]):
dept[data[10]][1] = data[14]
except TypeError:
continue
or to
import collections
dept = collections.defaultdict(lambda: [1000000000.00, 0.00])
for data in dictionary["data"]:
try:
if float(data[14]) < float(dept[data[10]][0]):
dept[data[10]][0] = data[14]
if float(data[14]) > float(dept[data[10]][1]):
dept[data[10]][1] = data[14]
except TypeError:
continue
Make the code easier to read by giving names to the
departmentName,
department,
and
salary.
Since
data[14]
is now mentioned in only once place,
I had to write
float
in only one place.
That ensures that every value entering the system is a
float,
so no further conversions are necessary.
It will also make it easier to print each salary with exacty two digits to the
right of the decimal point,
but we won’t do that now.
I changed the second
if
to
elif
because it is impossible for the same person to set a new record for
lowest salary
and
highest salary.
The
elif
avoids unnecessary work.
dept = collections.defaultdict(lambda: [1000000000.00, 0.00])
for data in dictionary["data"]:
try:
salary = float(data[14])
except TypeError:
continue
departmentName = data[10]
department = dept[departmentName]
if salary < department[0]:
department[0] = salary #sets a new record for lowest salary
elif salary > department[1]:
department[1] = salary #sets a new record for highest salary
Each value in the
data
variable represents a person,
so let’s rename this variable
person.
And let’s rename the
dept
dictionary to
departments,
to agree with the variable
department.
departments = collections.defaultdict(lambda: [1000000000.00, 0.00])
for person in dictionary["data"]:
try:
salary = float(person[14])
except TypeError:
continue
departmentName = person[10]
department = departments[departmentName]
if salary < department[0]:
department[0] = salary #This person set a new record for lowest salary.
elif salary > department[1]:
department[1] = salary #This person set a new record for highest salary.
In-depth study:
instead of saying
department[0]
and
department[1]
for the minimum and maximum salaries,
is there any way we could use
attributes
to say
department.minimum
and
department.maximum?
We’ve already come a long way towards making the script easier to read:
originally these two numbers were called
float(dept[data[10]][0])
and
float(dept[data[10]][1]),
with nested square brackets.
Was it worth it?