module 7

• Strings

  A data type that is a sequence of characters, which can include letters, numbers, punctuation, symbols, whitespace and special characters
• Strings must be enclosed in single or double quotes, e.g. 'this' or "that"
• Concatenation

  Joining strings together using the "+" operator
• Conversion to strings

  Other data types can be converted to strings, e.g. str(3.14) gives '3.14'
• String repetition

  Multiplying a string by an integer repeats the string, e.g. 'z' * 5 gives 'zzzzz'
• Strings as sequences

  Strings can be treated like sequences, allowing you to refer to characters by index, slice them, iterate through them, and check if a substring is present
• String immutability

  Strings are immutable - you cannot change individual characters, you can only create new strings
• String methods for testing

  • isupper()
  • islower()
  • isspace()
  • isalpha()
  • isdigit()
  • isalnum()
• String methods for searching

  • startswith()
  • endswith()
  • count()
  • find()
  • index()
  • replace()
• String methods for manipulation

  • lower()
  • upper()
  • lstrip()
  • rstrip()
  • strip()
  • ljust()
  • rjust()
  • center()
  • splitlines()
  • split()
  • join()
• "Chaining" methods

  Joining multiple string methods together in one statement to perform a sequence of operations
• Some programming languages have fewer built-in string manipulation functions compared to Python, requiring more manual approaches
• Dictionaries

  Another data structure in Python, like associative arrays or maps, where items are identified by unique keys rather than indexes
• Dictionaries

  • Mutable
  • Keys are usually strings that act as names or labels for the values
  • Items have no inherent order
• Creating dictionaries

  1. Use curly braces {} to enclose key-value pairs

  2. Separate keys and values with colons :

  3. Separate multiple pairs with commas ,
• Referencing dictionary items

  Use the key in square brackets [] to access the corresponding value
• ECU unit code

  1. 2 digits, dash or slash, 1-2 digits, dash or slash, 2-4 digits
• Date

  17
• Dictionary

  A data structure available in Python
• Dictionaries

  • Like lists, they are mutable (you can change the content)
  • Often known as "associative arrays" or "maps"
  • Items in a dictionary are identified by a "key" that you specify
  • Keys are usually strings
  • Items in a dictionary have no order
• Key-value pairs

  Items in a dictionary are often referred to as "key-value pairs"
• Dictionaries

  A collection of variables, each with a name (key) and a value
• Creating Dictionaries

  1. Dictionaries are created using curly braces

  2. Use the key to refer to an item in a dictionary
• Adding, Changing and Removing Dictionary Items

  1. Adding and changing items involves assigning a value to a key

  2. Use "del" to delete an item from a dictionary, using its key
• Dictionaries

  • The "in" comparison operator looks for a key, not a value
  • len() tells you how many items (key-value pairs) are in a dictionary
  • Dictionaries can have items and keys of different data types
• Looping through Dictionaries

  1. Looping through a dictionary using "for" works its way through the keys

  2. You can use the "items()" method to get both the key and the value
• Dictionary Methods

  • keys()
  • values()
  • items()
  • get(key[, default])
  • pop(key[, default])
  • popitem()
  • clear()
• Dictionary Method Examples

  • phones.keys()
  • phones.values()
  • phones.items()
  • phones.get('Leisa', 'No such key.')
  • phones.pop('Greg', 'No such key.')
  • phones.popitem()
  • phones.clear()
• Common Dictionary Usage

  Dictionaries are often used to store multiple different details about a thing, rather than storing multiple named instances of the same thing
• Dictionaries implement a data structure known as an "associative array" or "hashes" in many languages
• Dictionaries

  • Dictionaries are mutable (they can be changed) and they are unordered (the items have no "position" in the dictionary)
  • Keys are usually strings that serve to name or label the item
  • The keys in a dictionary are unique – trying to add another item with the same key will just overwrite that item
  • KeyError is raised if you refer to a key that does not exist
• Set

  A data structure available in Python
• Sets

  • The values in a set must all be unique (different)
  • Sets are unordered and the items have no keys or indexes
  • Sets are mutable – you can add and remove items
  • The values in a set can be of different data types
• Sets are a fundamental concept of mathematics
• Creating and Manipulating Sets

  1. Sets can be created in two ways – curly braces or the "set()" function

  2. "add()", "remove()" and "update()" manipulate the set
• Working with Sets & Set Methods

  • len(), "in" and "for" all work as you would expect
  • Set methods exist for common mathematical comparisons
  • You can use special operators instead of the methods
  • There are also methods/operators to find out if a set is a subset or superset of another set
• Sets are unordered collections of unique values
• Sets are a data structure that many languages do not offer
• When you need to keep track of a unique collection of values, sets are a very convenient way of doing so
• String testing, manipulating and searching is important, and Python gives you quite a few convenient ways to do it