📝Week 3 - Lab Intro

In this lab introduction we will briefly revisit some of the key topics from lecture and discuss the map function, which is used in the lab assignment.

Strings

The string data type stores a string of characters. Create a string by enclosing text in single or double quotes.

s1 = "This is an example string"
s2 = 'So is this'

Find the string length with len().

alphabet = "abcdefghijklmnopqrstuvwxyz"
print(len(alphabet))

26

You can slice strings by supplying indices in square brackets.

To slice a list L from a start index start up to (but not including) index stop with a step size of step, do the following:

L[start:stop:step]

# slice from index 0 up to (not including 5)
print(alphabet[:5]) 

# slice from index -3 to the end
print(alphabet[-3:]) 

# slice from index 0 to the end, stepping by 2
print(alphabet[::-1])

abcde
xyz
zyxwvutsrqponmlkjihgfedcba

You can use f-string formatting to easily include variable values in a string

year = 2023
year_message = f"The current year is {year}."

print(year_message)

The current year is 2023.

Lists and dictionaries

Lists are ordered collections of data. Dictionaries are a data structure that have (key, value) pairs.

# this is a list
L = ["abc", 42, True] 

# this is a dictionary
D = {
    "color": "green",
    "number": 12,
    "result": True
}

Square brackets are used to access values in a list or dictionary.

# get the list item at index 1
print(L[1])

# get the dictionary item at key "color"
print(D["color"])

42
green

Map function

We can use the map function to apply the same function to all elements of a list.

Example: squaring a list of numbers

# a simple fucntion that squares a number
def square(x):
    return x*x 

L = [0,1,2,3,4,5,6,7,8,9,10]

print(map(square, L))

<<<<<<< Updated upstream

<map object at 0x7f85170d9c60>
=======
<map object at 0x1097329e0>
>>>>>>> Stashed changes

The map function returns a map object that can be converted to a list as follows:

squared_L = list(map(square, L))
print(squared_L)

[0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100]