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Python Notes

Arithmetic

  • +

  • -

  • *

  • /

  • % modulo

  • myvar *= 0.9 90% of myvar

  • myvar -= 3 subtract 3 from myvar

Variables

  • mynum = 1234
  • int integer
  • float float
  • type check type of object
  • mynum = 1.3 creates a float variable
  • bol True or False
  • types can be converted
    • str() convert to string
    • float() convert to float
    • ...

Strings

  • mystring = "Test String"
  • len(mystring) length of string
  • mystring[0] - python uses indexing for string [0] returns the first character
  • print("var1 = {} and var2 = {}".format(var1,var2)) print format strint
  • split can be used to split strings into lists

Tipps and Tricks

  • Use bpython to test out little snippets of code. In comparison to python's standard interactive shell it offers command completion and function parameter view.
  • Use https://www.hackerrank.com/ for coding challenges

Lists

  • Sample liste: list_of_random_things = [1, 3.4, 'a string', True]

  • Lists can be accessed with list[0] up until list[len(list)-1]

  • When using slicing, it is important to remember that the lower index is inclusive and the upper index is exclusive.

Therefore, this:

list_of_random_things = [1, 3.4, 'a string', True] list_of_random_things[1:2] [3.4]

  • Lists are mutable
  • len() length of list
  • max() max element of list
  • min() smallest element of list
  • sorted() sorted list
  • join() join list elemnts to string
  • append() add something to a list

Tuples

  • Store related types of information
  • Ordered collection of objects
  • Immutable (no adding or removing items)
  • Saves processing power
dimensions = 10, 20, 30 			# assigning a tuple
length, width, height = dimensions 	# unpacking

Sets

  • Sets contain unique elemnts
  • add adds elements to a list
  • Sets are unordered
  • pop() removes one random element from the set
  • Sets are like mathematical sets. They support fast intersect, union operators.

Dictionaries

  • Store pairs
  • key and value store
  • keys do not need to be from the same datatype
  • lookup of values can be done using dict["lookupval"] or dict.get["lookupval"]. Get returns None if the lookup failes, a lookup with [] returns an error.
fruit_weight = {"apple": 5, "banana": 6}
fruit_weight["apple"]