CS150 - Fall 2012

CS150 - Fall 2012 - Class 6

apples and bananas
- http://www.youtube.com/watch?v=oacQL7UQtlk

admin
   - keep reading the book. We'll jump around a bit from the normal order of the book, so let me know if you find anything confusing.
   - Do the Lab prep for Friday! It's particularly important for this lab.
   - CS lunch on Friday in LaForce 121 (down the hall from Ross dining hall)

A quick review of strings from last time
   - we can index particular characters in the string using []'s. Indexing starts at 0
      >>> test = "a string"
      >>> test[0]
      'a'
      >>> test[2]
      's'
      >>> test[-2]
      'n'
   - we can get a substring (or part) of a string using slicing, giving a range of indices
      >>> test[2:4]
      'st'
      >>> test[1:6]
      ' stri'
   - We commonly want to iterate over the characters in a string. We can do this using range over the length of the string

      for i in range(len(test)):
         print test[i] # do something with test[i]

look at apples_and_bananas function in string_basics.py code
   - What does the function do?
      - iterates through each of the vowels and "replaces" them in the string with whatever letter was passed in

   - Strings are objects
      - objects represent data
      - but they also have "methods" that we can call on them
         - to call a method, we use the '.' notation

         >>> x = "this is a string"
         >>> x.upper()
         'THIS IS A STRING'
         >>> x.capitalize()
         'This is a string'
         >>> x.find("a")
         8
      - We can do this on anything that represents a string including variables like above, or on string literals:
         >>> "this is a string".upper()
         'THIS IS A STRING'
         >>> "this is a string".capitalize()
         'This is a string'
         >>> "this is a string".find("a")
         8

   - Strings are immutable!
      - test.replace("i", "a") does NOT change test
      - test.upper() does NOT changes test to upper case, but returns a new string that is the capitalize version

What other methods might we want for strings?
   - upper / lower
   - find
   - replace
   - startswith / endswith
   - isalnum
   - isalpha
   - isdigit
   - islower
   - isupper
   - Many more, look at the documentation: http://docs.python.org/library/string.html

Problem set 5 problem 1

A few examples to try
   >>> test = " A string"
   >>> test[4]
   't'
   >>> test[-5]
   't'
   >>> test[-10]
   Traceback (most recent call last):
    File "<string>", line 1, in <fragment>
   IndexError: string index out of range
   >>> test[0:2]
   ' A'
   >>> test[2:7]
   ' a stri'
   >>> test[7:]
   'ng'
   >>> test.lower()
   " a string"
   >>> test.upper()
   " A STRING"
   >>> test.find("i")
   6
   >>> test.find("ring")
   5
   >>> test.find("A string")
   1
   >>> test.find("banana");
   -1
   >>> " This is a string".find("i", 4)
   6
   >>> test.replace("s", "S")
   " A String"
   >>> test.replace("stri", "ris");
   " A rising"
   >>> "This is a string".replace("i", "")
   "Ths s a strng"
   >>> test.upper()[3:]
   "STRING"
   >>> test.upper().replace("i", "n").lower().find("n")
   7
   >>> test[0:3] + "longer " + test[3:]
   " A longer string"
   >>> test.startswith(" A ")
   True
   >>> test.startswith(" a")
   False
   >>> test.endswith("n");
   False
   >>> test.endswith("string");
   True
   >>> test.lower()[6:8].startswith("i")
   True