Healy Inkorperated

Notes and Other Thoughts

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Built-in Functions

Built-ins

  • sorted(iterable [,key] [,reverse] )
    • Returns a new sorted list based on the iterable in ascending order
    • Example: 
          x = [3,1,2]
    y = sorted(x)
    print(y) #[1,2,3]
    print(x) #[3,1,2]
      • .sort() sorts in place
  • len(thing)
    • Returns the length of thing
    • Works on strings, dictionaries, lists, tuples, and some other types, too
  • help(object)
    • Opens documentation for object
    • really useful in the interpreter
    • Quit with q
  • enumerate(iterable, start=0)
    • returns an object of type enumerate
      • yields tuples: (index, value)
    • keeps track of indices of object
    • Example: 
      for i,l in enumerate(something):
print( l," is at index", i)
  • range([start,] stop [,step=1])
  • Returns an object of type range
    • represents an immutable sequence of numbers
  • Useful for looping a set number of times
  • Don’t use this as a crutch
  • Bad: 
      L = [1,2,3]
  for i in range len(L):
print(L[i])
  • Good: 
      L = [1,2,3]
  for i in L:
print(i)
  • Using range adds bloat if you don’t need it
  • To mutate list: 
      L = [1,2,3]
  for i,v in enumerate L:
print(v)
L[i] = 10
    • Gives you indices without garbage and calculating length
  • input( [prompt] )
  • like cin; prompts the user for input

  • reads from stdin

  • “Constructors”
  • int(), float(), str(), dict(), etc.
  • Example: int(something_that_is_not_an_int)
  • Pitfalls:
    • int("100.0") will not work
    • int(float("100.0")) will work

Defining Functions

  • Basic syntax: 
    def <function name>(<arguments>):
      <body>
  • Arguments
  • Values must be provided for each positional argument in order
  • Arguments are always “[passed] by object reference”
  • wat. Prime test material 
      def func(a):
a.append("frog")
a = ["giraffe"]
a.append("submarine")
 x = ["apple"]
 y = x
 func(y)
 print(x) #[ "apple", "frog" ]
  • A function always returns something
  • If not explicitly, will implicitly return None.

Code Examples

  • Loops cont.
  • skipping values