Functions

Calvin (Deutschbein)

W6Mon: 30 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.
  • Whenever Python enters a new function, variables used within that function cease to exist when the function returns/ends. >>> x = 1 >>> def embiggen(): ... x = 2 ... x = x + 2 ... return ... >>> x 1 >>> embiggen() >>> x 1
  • "Embiggen's x" and "my x" are different x's, and things in "embiggen" do not affect "my x"

Taking a Walk through Vegas

    def Vegas(x): # what happens in Vegas etc etc y = 2 for i in range(3): DEBUG and print("Vegas: i = ",i,"| x = ",x,"| y = ",y) x += y return x
  • We can test it: >>> DEBUG = True >>> x = 3 >>> z = Vegas(x) Vegas: i = 0 | x = 3 | y = 2 Vegas: i = 1 | x = 5 | y = 2 Vegas: i = 2 | x = 7 | y = 2 >>> print("Mine: x = ", x, "| z = ", z) 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:str) -> bool: for i in range(len(word)): if word[i] in word[:i]: return False return True def no_vowels(word:str) -> bool: for letter in word: if letter in "aeiou": return False return True def longest_which_funcs(func) -> str: 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. >>> no_duplicates("aorta") False >>> no_vowels("why") True >>> longest_which_funcs(no_duplicates) 'ambidextrously' >>> longest_which_funcs(no_vowels) 'glycyls'

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.