Harvard CS50 Python Week 0 Functions

https://cs50.harvard.edu/python/2022/weeks/0/#week-0-functions

hello.py

code hello.py

print("hello, world")

Command-line Interface

python hello.py

Functions, Arguments, Side Effects

functions print() is a function
arguments inside of () a argument
side effects hello, world is a side effect

Bugs and Debugging

bugs a mistake is a bug

Return Values and Variables

input("What's your name? ")
print("hello, world")

input("What's your name? ")
print("hello, David")

name = input("What's your name? ")
print("hello, David")

name = input("What's your name? ")
print("hello, name")

name = input("What's your name? ")
print("hello,")
print(name)

comments

# Ask user for their name
name = input("What's your name? ")

# Say hello to user
print("hello,")
print(name)

pseudocode

# Ask user for their name

# Say hello to user

multiline comments

#
#
#
```
```

Comments and Pseudocode

# Ask user for their name
name = input("What's your name? ")

# Say hello to user
print("hello, " + name)

# Ask user for their name
name = input("What's your name? ")

# Say hello to user
print("hello,", name)

Multiple Function Arguments

str = string

print(*objects, sep=’ ‘, end=’\n’)

docs.python.org/3/library/functions.html#print

# Ask user for their name
name = input("What's your name? ")

# Say hello to user
print("hello,", end="")
print(name)

# Ask user for their name
name = input("What's your name? ")

# Say hello to user
print("hello,", name, sep="???")

Named Parameters

print(’hello, “friend”’)

print(”hello, \”friend\””)

Escaping Characters

# Ask user for their name
name = input("What's your name? ")

# Say hello to user
print(f"hello, {name}")

f-Strings

docs.python.org/3/library/stdtypes.html#string-methods

# Ask user for their name
name = input("What's your name? ")

# Remove whitespace from str
name = name.strip()

# Capitalize user's name
name = name.capitalize()

# another way and better way to capitalize
name = name.title()

# Say hello to user
print(f"hello, {name}")

# Ask user for their name
name = input("What's your name? ")

# Remove whitespace from str and capitalize user's name
name = name.strip().title()

# Say hello to user
print(f"hello, {name}")

# Ask user for their name
name = input("What's your name? ").strip().title()

# Say hello to user
print(f"hello, {name}")

String Methods

# Ask user for their name
name = input("What's your name? ").strip().title()

# Split user's name into first name and last name
first, last = name.split(" ")

# Say hello to user
print(f"hello, {first}")

split

int = integer

+, -, *, /, %

interactive mode

python

exit()

Integers and Operators

code calculator.py

x = 1
y = 2

z = x + y

print(z)

python calculator.py

x = input("What's x? ")
y = input("What's y? ")

z = x + y

print(z)

python calculator.py
What's x? 1
What's y? 2
12

Type Conversion

x = input("What's x? ")
y = input("What's y? ")

z = int(x) + int(y)

print(z)

x = int(input("What's x? "))
y = int(input("What's y? "))

print(x + y)

calculator.py

x = float(input("What's x? "))
y = float(input("What's y? "))

print(x + y)

python calculator.py
What's x? 1.2
What's y? 3.4
4.6

docs.python.org/3/library/functions.html#round

round(number[, ndigits])

x = float(input("What's x?"))
y = float(input("What's y?"))

z = round(x + y)

print(z)

python calculator.py
What's x? 1.2
What's y? 3.4
5

Floating Point Values

python calculator.py
What's x? 999
What's y? 1
1000

x = float(input("What's x?"))
y = float(input("What's y?"))

z = round(x + y)

print(f"{z:,}")

python calculator.py
What's x? 999
What's y? 1
1,000

Numeric Formatting

x = float(input("What's x?"))
y = float(input("What's y?"))

z = x / y

print(z)

x = float(input("What's x?"))
y = float(input("What's y?"))

z = round(x / y, 2)

print(z)

x = float(input("What's x?"))
y = float(input("What's y?"))

z = x / y

print(f"{z:.2f}")

Division

def

name = input("Whats's your name? ")
hello()
print(name)

def hello():
    print("hello")

name = input("Whats's your name? ")
hello()
print(name)

def hello(to="world"):
    print("hello,", to)

hello()
name = input("Whats's your name? ")
hello(name)

def main():
    name = input("Whats's your name? ")
    hello(name)

def hello(to="world"):
    print("hello,", to)

main()

Defining Functions

def main():
    name = input("Whats's your name? ")
    hello()

def hello():
    print("hello,", name)

main()

scope

def main():
    x = int(input("What's x? "))
    print("x sqaured is", square(x))

def square(n):
    return n * n
    return n ** 2 # same
    return pow(n, 2) # same

main()

Return Values

Week 0 Functions

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