Functions

Calvin (Deutschbein)

W6Mon: 29 Sep

Announcements

• By tonight 11:59 PM: "Project 1: Wordle"
  • My late policy is "no".
  • Sunday PM: ~40% have submitted no work.
    • We had work time in every class period last week!
  • QUAD Center open 6 PM to 9 PM (and there are more of them than me).
• Midterm on Friday.
  • Practice Exams posted
  • The next two days should be helpful on particularly questions 2-4.
  • There is a practice exam on Canvas where the exam will be hosted.

Today

• Function "Review"

Function "Review"

• A function is a named code block.
  • Prevents typos
  • Organizes thinking
• Some reminders about vocabulary:
  • Invoking or running a function by name is known as calling that function.
  • When calling a function, pass information to a function using arguments or parameters.
  • When a function completes its block of code, it returns to its caller.
  • The function gives information back to the caller by returning a result
• About use:
  • Functions cannot be used before they are defined.
  • Code after a return is never runned (the function "ends" at return)

"Messy" or "Dangerous" returns

• If code works, it works.
• But clear thinking will serve you life/school etc.
• Work directly with the boolean values when possible
• Try not to code patterns like the following: def is_divisible_by(x, y): if x % y == 0: # just return here instead of 'if' return True else: return False
• Generally speaking, we don't need to write out "True" if is_divisible_by(i,7) == True: # remove '== True' print(i)

Argument/Parameter Purposes

• Often functions should work in more than one case.
• E.g. "What is the longest no-repeat word in a certain language (not just English).
  • Imagine you were trying to accomplish the task yourself!
  • What is the minimum amount of information you would need to know?
• There is always a balance
  • More parameters makes your function more general, to be used elsewhere
  • More parameters are tedious and potentially error prone to enter if unnecessary

Embiggen

• Functions can contain their own variables. def embiggen(): x = 2 x = x + 2 return x = 1 print("Before:", x) embiggen() print("After:", x)
• "Embiggen's x" and "my x" are different x's, and things in "embiggen" do not affect "my x" x = 1 Before: 1 After: 1

Taking a Walk through Vegas

def Vegas(x): # what happens in Vegas etc etc y = 2 for i in range(3): print("Vegas: i = ",i,"| x = ",x,"| y = ",y) x += y return x x = 3 z = Vegas(x) print("Mine: x = ", x, "| z = ", z)
• We can test it: Vegas: i = 0 | x = 3 | y = 2 Vegas: i = 1 | x = 5 | y = 2 Vegas: i = 2 | x = 7 | y = 2 Mine: x = 3 | z = 9

Summary of a Function Call

• Evaluate the arguments in the context of the caller
print(2 + 2) # same as print(4)

Summary of a Function Call

• Evaluate the arguments in the context of the caller
print(2 + 2) # same as print(4)
• Copy argument to the corresponding parameter variable
def double_print(str): print(2 * str) double_print("mur") # same as print(2 * "mur")

Summary of a Function Call

• Evaluate the arguments in the context of the caller print(2 + 2) # same as print(4)
• Copy argument to the corresponding parameter variable double_print("mur") # same as print(2 * "mur")
• Evaluate statements in the function body, using the variables named within the function. def print_n_times(x, str): # n is 2, not 3, because "my n" and "double print n" differ print(x * str) n = 3 print_n_times(2, "mur") # same as print(2 * "mur")

Summary of a Function Call

• Evaluate the arguments in the context of the caller print(2 + 2) # same as print(4)
• Copy argument to the corresponding parameter variable double_print("mur") # same as print(2 * "mur")
• Evaluate statements in the function body, using the variables named within the function. n = 3 print_n_times(2, "mur") # same as print(2 * "mur")
• On 'return', compute the return value and substitute that value in place of the function call def repeat_n_times(x, str): return x * str s = repeat_n_times(2, "mur") # same as s = 2 * 'mur' print(s) # prints "murmur"

Scope

• When Python encounters a variable name in a program, it looks for where the variable was defined in an expanding search:
  • Local - Parameters/arguments or other variables within some function. Like letters within "enter_action".
  • Enclosing - Names inside a a calling function - like 'gw' within "enter_action"
  • Global - Things outside of any function, perhaps imported, like 'ENGLISH_WORDS'
  • Built-in - Things always defined everywhere, like "print" etc.
• The part of a program in which a name is defined in called its scope
• Always define a function or variable before you use it.

Scope

• Functions are just a special kind of variable. def no_duplicates(word): for i in range(len(word)): if word[i] in word[:i]: return False return True def no_vowels(word): for letter in word: if letter in "aeiou": return False return True def longest_which_funcs(func): candidate = "" for word in ENGLISH_WORDS: if len(word) > candidate and func(word): candidate = word return candidate

Scope

• Functions are just a special kind of variable.

  print(no_duplicates("aorta")) print(no_vowels("why")) print(longest_which_funcs(no_duplicates)) print(longest_which_funcs(no_vowels))

  False True ambidextrously glycyls

• We can use a function as the input to a function.

Announcements

• By tonight 11:59 PM: "Project 1: Wordle"
  • Sunday PM: ~40% have submitted no work.
    • We had work time in every class period last week!
  • QUAD Center open 6 PM to 9 PM (and there are more of them than me).
• Midterm on Friday.
  • Practice Exams posted.
  • The next two days should be helpful on particularly questions 2-4.
  • There is a practice exam on Canvas where the exam will be hosted.
  • More on Wednesday.