UTOSC 2008/90 percent of the Python you need to know (in 90 minutes)

Matt Harrison http://panela.blog-city.com

The Zen of Python:

import this

show memebers (attributes, functions) of instances:

dir()

show docs for modules/classes/functions

help()

help("".zfill)

Variables can point to anything:

my_var = "a string"
my_var = 42  # an int

Number very similar to other languages. No int overflow

Interpreter

>>> 2.97 * 94.2
279.774

Print variable

nums=5
nums

Strings:

hello = 'hello'
hello = "hello"
hello = """this is a
  paragraph and she said "hi" and it was good"""

String formattting:

 var = "is %s " % "matt"
 var = "is %d " % 20

Functions of string?

dir("")

Lists (mutable) and "tuples" (non-mutable)

alpha = ["a", "b"]
alpha.append("c")

alpha = ("a", "b")

Functions of a list?

dir([])

Slicing:

 alpha = ["a", "b", "c"]
 print alpha[0:1]  # 0 to 1
 print alpha[0:3:2]  # 0 to 3, every other one
 print alpha[1::2]  # ever other one

Range:

range(5)  # generate numbers 0 to 4
range(start, end, count)
range(99, 1, -1)

Dictionaries (hash maps, or associated arrays)

person = {"name": "bob", "age": 29}
age = person["age"]

Functions of dictionary:

dir({})

Functions:

def my_func(param_1, param_2):
  """ doc string """
  return param_1 + param_2

Functions can have default values:

 def add(num, add=5):

Return true if gymnast older than 16:

def is_16(year):
  return (2009 - year) >= 16

Conditionals:

if x > 90:
  grade = "A"
elif x > 80:
  grade = "B"
else:
 grade = "C"

While (no switch - use dictionary):

cap = {"utah": "salt lake", "arizona": "phoenix"}
if state in capitals:
  print "cap of %s is %s" % (state, cap[state])
else:
 print "not there"

Loops:

for item in range(10):
  print item

Break out of loop with break and continue

Indexes, use enumerate;

anim = ["a", "b", "c"]
for index, value in enumerate(animals):
  print value, index

Return a list of numbers squared:

def squared(numbers):
   results = []
   for num in numbers:
     results.append(num * num)
   return results

Open file:

fin = open("food.txt")
for line in fin:
  # do stuff
fin.close();

Write to file:

fout = open("bar.txt", "w")
fout.write("hi")
fout.close()

Comma at end of print statement won't add new line

print "hi",

Print integers to file:

fin.open("out.txt", "w")
for i in range(100):
  fin.write(str(i))  # cast to string
fin.close()

Class:

 class Hello(object):
   "doc string"
   
   # or

   """ 
     docs as paragraph
   """

   def __init__(self, name):
     self.name = name

   def talk(self):
     print "stuff"

   @staticmethod
   def main():
     print "Hello World"

Hello.main()

h = Hello("thing")
h.talk()

Subclass:

 class hi(Hello):
   def talk(self):
      print "something else"

Try catch:

try:
  ...
except KeyError, e:
  ...
except Exception, e:
  ...

Raise execption:

raise Exception("my error")