Terminology

• String vs. char array
• Datatype
• Sequence - Index, slicing and iteration
  • Sequences of values can be described by a start point and an endpoint
  • They support the membership operator (in), the size function(len()) and slicing
  • Slicing: given a sequence, you can get any part of it as a new sequence
  • Eg. range(0, 5) means [0:5) which means the values 0, 1, 2, 3, and 4
  • Sequences are iterable
• Immutable
  • No assignment to elements allowed
  • Methods return new objects
• Function signature
• HTML

  <h1>This is a heading</h1>
  <p>This is a paragraph</p>
  <p>A paragraph with <a href="http://find-santa.eu">a link to my homepage</a>.</p>
  

• Library
  • Collection of pre-built code we can use
  • Using them avoids duplicate work (and they are designed by professionals)
  • Libraries provide services to independent programs
  • Standard library vs. third party libraries
  • "...we again and again avoid doing complicated work and instead find simpler solutions - often relying on library facilities. That's the essence of programming: the continuing search for simplicity." – Bjarne Stroustrup

String Operations

• ", ', """, '''
• S.split([sep[, maxsplit]]) -> list of strings
• S.upper() -> str
• Using string functions

• #!/usr/bin/env python3
  
  a_string = "What a beautiful snake!"
  a_string.upper()
  print(a_string)
  a_string = a_string.upper()
  print(a_string)
  
  print()
  print(a_string.split())
  a_string = "Steve, Paul, Susan, Anna, Peter, Amy"
  print(a_string.split(','))
  

• IPython shows us what we can do with a string
  • Open Terminal

Substrings

• The first element of any sequence has the index 0
• A second index points to the element after a slice
• Start and end are available by skipping an index
• Using slicing

• #!/usr/bin/env python3
  
  a_string = "What a beautiful snake!"
  char = a_string[0]
  char = a_string[1]
  char = a_string[-1]
  char = a_string[-3]
  substring = a_string[1:5]
  substring = a_string[1:-3]
  substring = a_string[:-2]
  substring = a_string[-2:]
  result = a_string[::2]
  

• Python 3 Video Tutorial - Strings
• Python 3 Video Tutorial - String Formatting

For Loops

• Iterate over the elements of a sequence
  • Each time the body of a for loop runs, a variable is set to the next element of a sequence

• For loop syntax

• #!/usr/bin/env python3
  
  a_string = 'What a beautiful snake!'
  for char in a_string:
      print(char)
  for index, char in enumerate(a_string):
      print(f'{index:2}: {char}')
  

• Simple counting

• #!/usr/bin/env python3
  
  TOTAL = 0
  for i in range(5):
      TOTAL += i
  
  for _i in range(5):
      print("Repeated action")
  
  sum_even = 0
  for i in range(10, 0, -2):
      sum_even += i
  

• Python 3 Video Tutorial - For Loops

Reading Files

1. Open the file with open(.)
2. Read the file with read(), readline(), readlines() or iterate over its content
3. Close the file with close() or implicitly (end of with)
4. However, the newer and better way to read files is (instead of the above!)

   with open(filename, encoding='utf-8') as f:
       for line in f:
           print(line, end="")
   

   note: filename is a variable that needs to contain a string denoting a filename

• Python 3 Video Tutorial - Reading and Writing Files