CSE 160 Section 5
File I/O and Dictionaries!
Logistics
Lecture Review: File I/O
File I/O
my_file = open(filepath)
for line_of_text in my_file:
# process line_of_text
my_file.close()
Split
Example:
O
Output:
line_of_text = “you’re going to be amazing”
x = line_of_text.split()
print(x)
[“you’re”, “going”, “to”, “be”, “amazing”]
Split
Example:
O
Output:
line_of_text = “you’re,going,to,be,amazing”
x = line_of_text.split(“,”)
print(x)
[“you’re”, “going”, “to”, “be”, “amazing”]
Lecture Review: Dictionary
Dictionary
Collection of key-value pairs
Dictionary
heights = {"Ella": 68,
"Martin": 72,
"Lilly": 49,
"William": 50,
"Simon": 70}
print(heights["Lilly"]) # 49
print(heights["Wen"]) # KeyError
heights["Wen"] = 63 # Add a key-value pair
heights["Lilly"] = 50 # Update value
print(heights["Lilly"]) # 50
Dictionary
# print out all keys
for key in heights.keys():
print(key)
# print out all values
for value in heights.values():
print(value)
# print out keys and values
for (key, value) in heights.items():
print(key, value)
# another method
for key in heights:
value = heights[key]
print(key, value)
Dictionary built-in functions
Operation (dictionary d) | Description |
d.items() | Returns a list containing a tuple for each key-value pair. |
d.keys() | Returns a list of the dictionary keys. |
d.values() | Returns a list of all values in the dictionary. |
d.pop(key) | Removes the element with the specified key. |
d.popitem() | Removes the last inserted key-value pair. |
d.update(dict) | Updates the dictionary with the specified key-value pairs. |
d.copy() | Returns a copy of the dictionary. |
d.get(key) | Returns the value of the given key. |
Additional Operations
Section Handout Problems
Problem 1
You have a file named students.txt where each line contains a student's name and age separated by a comma, like this:
Alice,20�Bob,22
Write a program that reads the file and prints each student's name and age separately.
Example output:
Name: Alice, Age: 20
Problem 1
students_file = open("students.txt"):
for line in students_file:
parts = line.split(",")
name = parts[0]
age = parts[1]
print("Name:", name, "Age:", age)
students_file.close()
Problem 2
Write a function called count_words(filename) that reads the file and returns the total number of words across all lines. The file is formatted so that each line is a sentence.
For example, if you had a file quotes.txt that contains:
Hi my name is Annie.
Let’s learn Python!
The returned value would of count_words(“quotes.txt”) be:
8
Problem 2
def count_words(filename):
word_count = 0
my_file = open(filename):
for line in my_file:
words = line.split()
word_count += len(words)
return word_count
Problem 3
Create def get_squares(number_list) that accepts a list of numbers as a parameter, and returns a dictionary mapping each number in the list to its square.
For Example:
nums = [1, 4, 4]
get_squares(nums) returns {1:1, 4:16}
Problem 4
Write coldest_city(city_temperatures) that takes in a dictionary and return the city (key) with the lowest temperature (value).
For Example:
city_temperatures = {‘Seattle’: 36, ’Cupertino’:39, ‘New York’:57}
coldest_city(city_temperatures) => returns “Seattle”
Problem 5 Part a
Write function def pokemon_types(pokemon_dict) that takes parameter pokemon_dict and returns a new dictionary mapping each type of pokemon to the number of pokemon in pokemon_dict with that type.
For example, when
pokemon_dict = {"pikachu": "electric", "charmander": "fire", "charizard" : "fire"}
pokemon_types(pokemon_dict) => returns {“electric” : 1, “fire” : 2}
Problem 5 Part b
Write def pokemon_types(pokemon_dict) that takes parameter pokemon_dict and returns a new dictionary mapping each type of pokemon to the list of pokemon with that type.
For example, when
pokemon_dict = {"pikachu": "electric", "charmander": "fire", "charizard": "fire"}
pokemon_types(pokemon_dict) returns =>
{‘electric’ : [‘pikachu’], ‘fire’: [‘charmander’, ‘charizard’]}