More With Lists Strings Tuples Sets And Py Charm

More on Lists

Some more available operations:

• ls3 = ls1 + ls2 concatenates lists and returns a new list

• ls1.extend(ls2) appends the values of a list to another list

• repeated_ls = ls * 3 returns a new list with the sequence of values repeated x number of times

• ls[-1] returns the value at the index of len(ls) - 1; useful for grabbing values at the end of the list

• ls[start_index:end_index] returns a slice of a list as a new list

  • start_index is optional and is included in slice (defaults to 0 if not included)

  • end_index is optional and is NOT included in slice (defaults to len(ls) if not included)

  • Pro tip: A common way to create a copy of a list is via ls[:]

  • Another pro tip: You can set values at multiple indices at once via...

    • ls[1:4] = [1,3, 5]

Two forms of equality testing:

• Check for same reference: ls1 is ls2

• Check for same values: ls1 == ls2

More on Strings

Think of strings like lists of characters. You can access characters at indices, except you just can't mutate them because strings are still immutable.

my_string = "Hello"
my_string[1] # returns "e"
my_string[1] = "a" # throws error

Instead, to mutate a character, a good technique is to convert to a list and then join:

my_string = "Hello"
chars = list(my_string)
chars[1] = "a"
my_new_string = "".join(chars) # returns "Hallo"

Note: join takes the string as the separator and the list as the argument.

Just like a list, you can slice strings too:

my_string = "Hello"
my_string[0:2] # returns "He"

Here's some useful string methods: see docs.

Tuples

Tuples are:

• Sequence of values

• Values do not have to be the same type

• Immutable

Syntax for initializing tuple:

# All valid ways of creating a tuple:
tuple1 = ("hello", 1, False)
tuple2 = "hello", 1, False
tuple3 = tuple(["hello", 1, False]) # converts list/string to tuple

To access values in a tuple:

t = "a", "b", "c"

# Index access
t[0]

# Multiple variable assignment
a, b, c = t

Pro tip: Tuples are very useful when returning multiple things from a function at once.

def min_and_max(ls):
  return min(ls), max(ls)

Sets

Sets are collections with the following features:

• Unordered

• Do not contain indices

• Do not allow repeated elements

• Values do not have to be the same type

• Mutable

Syntax for initializing a set:

set1 = { 1, "hello", False, "hello" } # "hello" only appears once
set2 = set([1, "hello", False, "hello" ]) # "hello" only appears once

empty_set = set() # empty sets cannot be initialized with {...}

Operations for sets:

• Iteration: for item in set:

• Adding element: set.add("hello")

• Removing element: set.remove("goodbye")