Lesson 5 Notes: Pre-Made Functions

• So, what’s a function?
  • Function = defined set of instructions
  • Set of code that you can use over and over
  • May be created by you or imported from module
  • Example
    • Math calculations (log, sin, cos, tan, exp, hypot)
    • Randomization, inputs, changing strings
    • User made code to recycle
• Using Ready-Made Functions
  • Find out what is available
    • Documentation
    • http://www.python.org/doc/current/modindex.html
  • Import appropriate module
    • import module_name
  • Use function call to use function
    • module_name.function(arguments)
• Making a Function Call
  • import math
  • math.hypot(8,9)
    • math – Module that contains math functions, including hypot() function to find the length of a hypotenuse.
    • . – Separates module from function
    • hypot – Name of function
    • () – Place for arguments. Required for all function calls, whether there are arguments or not.
    • 8,9 – Numbers being sent to function for processing. In this example, 8 and 9 are the length of the two legs of a triangle and the function will use the Euclidian formula to find the third.
• Look Familiar?
  • input() is a built-in function
    • input is the name of the function
    • input() accepts a string in the () which it will display as the prompt
  • Raw_input() is another built-in function
    • raw_input() is the name of the function
    • raw_input accepts a string in the () which it will display as the prompt
• For Best Results
  • Some functions are built-in and do not need a module imported.
  • Some functions take arguments in (), others do not, but all need the ().
  • If you aren’t sure what goes in the (), type the first ( in Idle and wait a few seconds. A tip will show up to remind you.
  • Functions can take variables as arguments
• Some Built In Functions
  • float() – Converts a string or other number to a floating point number
  • int() – Converts a string or other number to a plain integer.
  • long() – Converts a string or other number into a long number.
  • str() – Converts a number into a string
• Some More Built In Functions
  • divmod(x,y) – Returns the result of x/y and x%y
  • len(s) – Returns the length a string or other data type
  • pow(x,y) – Returns x to the power y
  • range(start,stop,step) – Returns a set of numbers from “start” to “stop”, counting by “step”.
  • Round(x, n) – Return the floating point value x rounded to n digits after the decimal point. If n is omitted, it defaults to zero.
• Some Math Module Functions
  • acos(x), asin(x),atan(x) – arc cosine, arc sine, and arc tangent of number.
  • cos(x), sin(x), tan(x) – cosine, sine, and tangent of number.
  • log(x), log10(x) – Natural log and base 10 log
  • pow(x,y) – X raised to the power Y
  • hypot(x,y) – Returns length of hypotenuse for triangle with sides of length x and y.
• Some String Module Functions
  • capitalize() – capitalize first word
  • capwords() – capitalize all words
  • lower() – all letters lower case
  • upper() – all letters upper case
  • replace(string, old, new) – replace all “old” words in “string” with “new” words
  • center(string, width), rjust(string, width), ljust(string, width) – center, right justify, or left justify the string in a field of a given width.
• Some Random Module Functions
  • randrange(start,stop,step) – get a random number between the “start” number and “stop” number. “Step” is optional.
  • choice(sequence) – randomly select an object in the sequence.
• Some Other Modules and Functions
  • Time
    • sleep(x) – have computer sleep or pause for a given number of seconds.
  • Calendar
    • prcal(year) – Print calendar for year
    • prmonth (year,month) – Print calendar for month
• Review
  • What are functions?
  • What are modules?
  • What must you know about a function before you use it?
  • What is the correct way to write a function call?
  • Give an example of a pre-built function.