# IMPORT DATA FILES USED BY THIS NOTEBOOK
import os, requests
file_links = [("data/ChemicalSymbols.csv", "https://ndcbe.github.io/cbe-xx258/data/ChemicalSymbols.csv")]
# This cell has been added by nbpages. Run this cell to download data files required for this notebook.
for filepath, fileurl in file_links:
stem, filename = os.path.split(filepath)
if stem:
if not os.path.exists(stem):
os.mkdir(stem)
if not os.path.isfile(filepath):
with open(filepath, 'wb') as f:
response = requests.get(fileurl)
f.write(response.content)
1.5 List, Dictionaries, and Enumeration¶
Reference: Chapters 2 and 5 of Computational Nuclear Engineering and Radiological Science Using Python, R. McClarren (2018)
1.5.1 Learning Objectives¶
After studying this notebook, completing the activities, and asking questions in class, you should be able to:
1.5.2 Lists¶
You can also do other fun stuff with for loops. For instance, you can have the control variable take on non-numeric things:
#silly hat code
hats = ["fedora","trilby","porkpie","tam o'shanter",
"Phrygian cap","Beefeaters' hat","sombrero"]
days = ["Monday","Tuesday","Wednesday","Thursday",
"Friday","Saturday","Sunday"]
count = 0
for today in hats:
print("It is",days[count],"and I will wear a",today)
count += 1
Notice what else we did here: we defined a list called days that contained strings for the names of the days of the week. Inside our for loop we had a numeric variable that kept track of what number the day of the week was (0 for Monday in this case). Then when we access days[count] it returns the string in position count.
We can go one step beyond and plan our wardrobe a month in advance using random numbers. The code below generates a random integer between 0 and 6:
import random
my_random_number = round(random.uniform(0,6))
print(my_random_number)
#silly hat code
import random
hats = ["fedora","trilby","porkpie","tam o'shanter",
"Phrygian cap","Beefeaters' hat","sombrero"]
days = ["Monday","Tuesday","Wednesday","Thursday",
"Friday","Saturday","Sunday"]
# loop over 30 days
# YOUR SOLUTION HERE
Lists are like vectors in MATLAB, except, as you can see above, we can store more than just numbers in them. We will talk about using a package numpy to represent vectors and matrices next class session.
## Attempt 1
N = [1, 2, 3, 4, 5, 6, 7, 11]
for i in range(len(N)):
print(i+1)
# YOUR SOLUTION HERE
## Attempt 2
N = [1, 2, 3, 4, 5, 6, 7, 11]
for i in range(len(N)):
print(N[i])
# YOUR SOLUTION HERE
## Attempt 3
for i in range(0,10):
print(i)
# YOUR SOLUTION HERE
1.5.3 Dictionaries¶
So far, we have used lists to store a sequence of numbers or more generally Python objects. Lists (and NumPy arrays - stay tuned) access elements by position and have an inherent ordering.
A dictionary is a set of key : value pairs. You can think of a dictionary as a fancy list that instead of accessing via the position, you access using a key.
#simple dictionary
days_of_week = {"M":"Monday", "T":"Tuesday",
"W":"Wednesday", "R":"Thursday",
"F":"Friday", "S":"Saturday",
"U":"Sunday"}
print("Key M gives", days_of_week["M"])
print("Key R gives", days_of_week["R"])
# YOUR SOLUTION HERE
Calling days_of_week.keys() returns a special list of the keys of the dictionary.
print(days_of_week.keys())
We can also check if G is a valid key for the dictionary.
print("G" in days_of_week.keys()) #is G a key in days_of_week?
Main idea: With dictionaries, we access elements using the key. In contrast, we access elements of strings, lists, and Numpy arrays using the position.
1.5.3.1 Example: Shopping List¶
- 1.5 bannas (pounds)
- 3 cans of soup
- 6 apples
- 2.3 pork tenderloin (pounds)
# YOUR SOLUTION HERE
1.5.3.2 Another Example: Chemical Symbols and Element Names¶
Below is code that parses ChemicalSymbols.csv and stores the data in dictionary.
import csv
element_dict = {} #create a blank dictionary
# this block will only execute if the file opens
with open('./data/ChemicalSymbols.csv') as csvfile:
chemreader = csv.reader(csvfile)
for row in chemreader: # have for loop that loops over each line
element_dict[row[0]] = row[1] # add a key:value pair
# Ask user to enter a chemical symbol
key = input("Enter a valid chemical symbol: ")
if key in element_dict:
print(key,"is",element_dict[key])
else:
print("Not a valid element")
We can also print out the dictionary.
print(element_dict)
element_dict
1.5.3.3 Dictionary of Dictionaries¶
We can make dictionaries even more powerful if we make a dictionary of dictionaries.
Top Level. Day of the week.
- Key: symbol "M", "T", etc.
- Value: Another dictionary!
Second Level. Data for each day.
- Keys: "name", "weekday", "weekend"
- Values: string, boolean (True or False), boolean
#simple dictionary of dictionaries
days_of_week = {"M":{"name":"Monday","weekday":True,"weekend":False},
"T":{"name":"Tuesday","weekday":True,"weekend":False},
"W":{"name":"Wednesday","weekday":True,"weekend":False},
"R":{"name":"Thursday","weekday":True,"weekend":False},
"F":{"name":"Friday","weekday":True,"weekend":False},
"S":{"name":"Saturday","weekday":False,"weekend":True},
"U":{"name":"Sunday","weekday":False,"weekend":True}}
print("The days that are weekdays are")
for day in days_of_week: #for loop over dictionary, loops over keys
if days_of_week[day]["weekday"] == True:
print(days_of_week[day]["name"],"is a weekday.")
print("The days that are weekend days are")
for day in days_of_week: #for loop over dictionary, loops over keys
if days_of_week[day]["weekend"] == True:
print(days_of_week[day]["name"],"is a weekend, whoop.")
Notice that when you loop over a dictionary in a for loop, the loop variable will get each of the keys of the dictionary.
The dictionary has been modified to include the day name in Spanish.
#more complicated dictionary of dictionaries
days_of_week2 = {"M":{"name":"Monday","weekday":True,"Spanish":"Lunes"},
"T":{"name":"Tuesday","weekday":True,"Spanish":"Martes"},
"W":{"name":"Wednesday","weekday":True,"Spanish":"Miércoles"},
"R":{"name":"Thursday","weekday":True,"Spanish":"Jueves"},
"F":{"name":"Friday","weekday":True,"Spanish":"Viernes"},
"S":{"name":"Saturday","weekday":False,"Spanish":"Sábado"},
"U":{"name":"Sunday","weekday":False,"Spanish":"Domingo"}}
# YOUR SOLUTION HERE
1.5.4 Enumerate¶
1.5.4.1 Lists¶
Let's see some syntax for growing lists.
# create a list with nothing
students = []
# add a student
students.append("Joe Smith")
# add another student
students.append("Jane Doe")
print(students)
How to loop for the list? Let's review.
# Approach 1
for s in students:
print(s)
# Approach 2
for i in range(len(students)):
print(i,": ",students[i])
Can simply the syntax? It is really convienent to access the index with i and the student with s.
for i, s in enumerate(students):
print(i,": ",s)
1.5.4.2 Dictionaries¶