built-in functions (slides)

CSC 110 Python Functions

Built-in Functions

• print()
• round()
• type()
• input()
• len()
• int()
• float()

Write a function

Write a Python function that does the following:

1. Its name is greeting
2. It takes two arguments, first_name and last_name
3. It returns a string with a greeting using first_name and last_name

print( greeting("Mickey", "Mouse") ) # Hello, Mickey Mouse!

input() function

• The input() function prompts the user to input text in the standard output
• Whatever is inside the parentheses in input() will be written to the standard output (without a trailing newline, which you can add using \n).
• The function then reads a line from input, converts it to a string (stripping a trailing newline), and returns that
• input() always returns a string

input("What's your name?\n")

Write a function

Write a Python function that does the following:

1. Its name is greeting_again with no parameters
2. It first prompts you to enter your first name
3. It again prompts you to enter your last name
4. It returns a string with the same greeting as greeting but replace with your first and last name

print( greeting_again() ) 

Write a function

def greeting(first, last):
    message = "Hello, " + first + " " + last + "!"
    return message

def greeting_again():
    first = input("Enter your first name:\n")
    last = input("Enter your last name:\n")
    message = "Hello, " + first + " " + last + "!"
    return message

def main():
    print(greeting("Mickey", "Mouse"))
    print(greeting_again())

main()

len() function

• The len() function can be used with many types – we will be using it with string for now
• It returns the number of characters in a string

character_count = len("Mickey")
print(character_count)

6

Write a function

Write a Python function that does the following:

1. Its name is count_characters
2. It takes three string arguments, a, b and c
3. It returns the total number of characters for all three strings

print( count_characters("hel", "lo", "world") ) # 10
print( count_characters("", "", "") ) # 0
print( count_characters(" ", " ", " ") ) # 3
print( count_characters("10", "2", "3") ) # 4

Write a function

def count_characters(a, b, c):
    return len(a) + len(b) + len(c)

def main():
    print( count_characters("hel", "lo", "world") ) # 10
    print( count_characters("", "", "") ) # 0
    print( count_characters(" ", " ", " ") ) # 3
    print( count_characters("10", "2", "3") ) # 4

main()

10
0
3
4

int() function

• The int() function can be used to convert a string to an integer type
• It only works if the string only contains digits

age = '35'
age_int = int(age)
print(type(age), type(age_int))

<class 'str'> <class 'int'>

float() function

• The float() function can be used to convert a string to a float type
• It only works if the string only contains digits and optionally a decimal point

age = '35'
age_float = float(age)
print(type(age), type(age_float))

<class 'str'> <class 'float'>

Write a function

Write a Python function calculate_year_born with no parameters. It prompts user to enter their age input().

It converts user’s age to integer and calculates (imperfectly) the year a person of age was born by subtracting age from 2025.

It returns an integer representing the approximate year person of age was born.

print( calculate_year_born() ) # user enters 60, function returns 1965

Write a function

def calculate_year_born():
    str_age = input("what's your age?\n")
    age = int(str_age)
    year_born = 2025 - age
    return year_born

def main():
    print(calculate_year_born())

main()

Write a function - solution

Write a Python function mars_weight with no parameters. It prompts user to enter their weight input().

Then calculate their weight on Mars using weight * 0.38.

It returns the weight on Mars rounded at integer.

print( mars_weight() ) # user enters 150, function returns 57

Write a function - solution

def mars_weight():
    str_weight = input("what's your weight?\n")
    weight = float(str_weight)
    mars_weight = weight * 0.38
    return round(mars_weight)

def main():
    print(mars_weight())

main()