Python beginner's body fat calculator

all of your functions seem to do the same thing with a different message, so why not condense them and take the message as a parameter?

def get_num(msg):
    num = None
    while num is None:
        try:
            num = float(raw_input(msg))
        except ValueError:
            print("Use a number, silly!")

    return num

and then

def output():
    x = get_num('Please give your weight (pounds): ')
    y = get_num('what is your current body fat percentage? (>1): ')
    z = get_num('What is your desired body fat percentage? (>1): ')
    A = (x*(y/100-z/100))/(1-z/100)
    B = x - A
    print("Your necessary weight loss is %.1f pounds, and \
your final weight will be %.1f pounds" % (A,B))
    more()

in your more function you can condense your ifs with the in operator

def more():
    again = raw_input("Calculate again? ")

    if again.lower() in ["yes", "y", "sure" , "ok", "", "okay"]:
        output()
    elif again.lower() in ["no", "n", "nah", "nope"]:
        end()
    else:
        more()

Do you have objects, "things" that have state and behaviour? I don't see any. So use functions as you do (perhaps improve the code format).

In getx, gety and getz there's no need to use global and return. Also, it would be better to use iteration rather than recursion, like this:

def getx():
    while True:
        try:
            return float(raw_input("Please give your weight (pounds): "))
        except ValueError:
            print("Use a number, silly!")

You might also want to use better function and variable names.

Yes, you definitely can. You can try something in the lines of:

class PersonData(object):
  def __init__(self):
    pass


  def getx(self):
    try:
        self.x = float(raw_input("Please give your weight (pounds): "))
    except ValueError:
        print("Use a number, silly!")
        self.getx()

.. and so on.

And then in your main program:

if __name__ == "__main__":
  person = PersonData()
  person.getx()
  person.gety()

... 

  A = (person.x * (person.y / 100 - person.z / 100))/(1 - person.z / 100)

If you get my drift. This is generally if you want to use classes. Otherwise see other answers :)

The code below condenses your script (fewer lines and redundancy when you remove the triple quote explanations). Honestly, using classes would complicate your function, so unless you need the classes for something else, just do all in the function. Also, typically it is better to not call globals unless you need to. For your purpose, unless there is more to the script, use local variables.

Your script suffers a lot from redundancy. It works fine, but there are easier ways to do it. Instead of reusing again.lower() ==, put all the desired responses into a list. Using 'is...in' checks if your variable is in you list (or string, etc). For example, if var in ["y", "yes"]:

You can further reduce your redundancy by making a function to do your try/except statements, but I used while statements to show another way to do it. You can then use continue (which resets back to the beginning) if there is an exception and use break to exit the loop if you try statement succeeds.

Note: I tested this on Pythonista for iOS using 2.7. I added in the triple quotes as explanations after confirming the script worked and using as is may throw an indentation error. Removing the triple quote explanations should run it properly.

""" Unless you are reusing variables, but it all in 
the same function"""

def output():
""" Put your inputs in a while statement. Continue on
exception and break otherwise"""
    while True:
      try:
         x = float(raw_input("Please give your weight (pounds): "))
      except ValueError:
          print("Use a number, silly!")
          continue
      break
    while True:
      try:
          y = float(raw_input("what is your current body fat percentage? (>1): "))
      except ValueError:
          print("Use a number, silly!")
          continue
      break
    while True:
      try:
          z = float(raw_input("What is your desired body fat percentage? (>1): "))
      except ValueError:
         print("Use a number, silly!")
         continue
      break
    A = (x*(y/100-z/100))/(1-z/100)
    B = x - A
    print("Your necessary weight loss is %.1f pounds, and \
your final weight will be %.1f pounds" % (A,B))

""" Like before put input into while statement"""

    while True:
      again = raw_input("Calculate again? ")

""" Condense your input options into an if in statement"""
      if again.lower() in ["yes", "y", "sure", "ok", "", "okay"]:
        output()

""" Unless No response is important, just use else
catchall"""
      else:
        print("Ok, see ya later!")
        break
output()