Exam Scheduled for Week 5 Monday 10am LH3

The String Data Type, Ch 4.1

• >>>type ("hi")
• >>>"hi" + "there" # string concatenation
• s = raw_input("Give me a name: ")
• String indexing: s[0], s[-1], s[-3], s[0:3], s[5:9]
• String repetition: s*3
• String as sequence: for ch in "Spam!": print ch,
• Calculating sequence length with an accumulator technique (mylen.py)
• len("hi there") # built-in string length function

Simple String Processing, Ch 4.2

• Strings are sequences of characters
• String loop on character sequence (stringLoop.py)
• Passing the string as a parameter (stringLoop.py)
• Another string loop using range(len(myString)) (stringLoop.py)
• Designing the username program p82 (username.py)
  1. Ask for first name (use raw_input)
  2. Ask for last name
  3. Concat together last name plus first letter of first name
• Tracing the username program
• Design a program to reverse a string. Use the accumulator design pattern. (reverse.py)
  1. Ask for a string s
  2. Initialize an accumulator rs to an empty string
  3. loop on each character in the string s
  4. Inside the loop concat each character at the beginning of the reverse string accumulator
• Tracing the reverse() program
• Design the reverse as a separate function from main() (reverse.py)
  • main()
    1. Ask for a name
    2. call a reverse function that returns a reversed name
    3. print the reversed name
  • reverse(s)
    1. initialize an accumulator to an empty string
    2. loop on each character in the string
    3. Inside the loop concat each character at the beginning of the reverse string accumulator
• Designing the month abbreviation program p84
  • Input: month number (1-12). Output: Month abbreviation, 3 letter.
  • Make all abbreviations into a long string months = "JanFebMar...Dec"
  • Note that months[0:3] is Jan, months[3,6] is Feb, etc.
  • Use the input number to calculate the start index of the abbreviation.
  • If n is the month then months[3*(n-1):3*(n-1)+3] is the abbreviation.
  • Print the selected string slice.
• Tracing the month abbreviation program

Strings, Lists, and Sequences, Ch 4.3

• Strings are sequences of characters.
• range[5,100,5] is a sequence of numbers
• Lists are sequences of anything
• mylist = [1,"Spam", 4, "U"] # note mixing of types is ok!
• Notes that we even have a sequence inside a sequence! (The strings).
• Slices work on lists just as strings, or any sequence.
• mylist[1:3] is ["Spam",4, "U"]
• The empty sequence is []
• Sequences can be changed! (Unlike strings, by the way)
• mylist[2] = "to" # Now look at mylist

• Rewrite the months.py program to be simpler (p86)
• Make the months variable be a sequence: months = ["Jan","Feb", ... ,"Dec"]
• Just index by n-1 now.

Encoding Characters and Strings, Ch 4.4

• Strings are sequences characters
• Characters are stored in memory words as numbers.
• Ascii characters codes are 8 bits, Unicode standards support up to 32 bits for character encoding, allowing for many, many character sets from many, many languages.
• functions ord("a") and chr(33) tranlate between characters and their numerical representation.
• Programming an encoder (encode.py)
• Tracing the encoder program
• String functions (p96)
• string.upper(s), string.lower(s) (pp94-95)
• string.split(s), string.join(ls) (pp92-95)
• Note the prefix name referring to the string library that is built in so you don't have to import it.
• Read and write the decoder program (p93) using string.split and eval.
• input("Enter a number: ") same as eval(raw_input("Enter a number: "))
• Use int(x) or float(x) instead of eval(x) (p99)

File Input and Output, Ch 4.6

• A simple and efficient way to read lines from a text file (p110 middle)

    infile = open("myfile.txt", 'r')   # infile is any name you want to chose
    for line in infile:                # infile has type File (a file variable)
      print line
    infile.close()       # note the dot notation for object related functions
  

• Read and write the userfile.py program p111
• Write the myfile.py program to print a file to the console.
• Note the double spacing ... why? Because the newline is in the file.
• Object oriented notation for calling functions of objects, infile.close()

Formatting Output using Strings, Ch 4.5.2

• Using str(x) to convert a number to a string.
• Read and write the dateconvert.py program (p100)
• Read and try the string formatting examples p104
• Rewrite the convertLoop.py program from lecture 3 to line up columns. (convertTable.py)