[Introduction to Udemy Python3 + Application] 18. List methods

** * This article is from Udemy "[Introduction to Python3 taught by active Silicon Valley engineers + application + American Silicon Valley style code style](https://www.udemy.com/course/python-beginner/" Introduction to Python3 taught by active Silicon Valley engineers + application + American Silicon Valley style code style ")" It is a class notebook for myself after taking the course of. It is open to the public with permission from the instructor Jun Sakai. ** **

■ List methods

◆.index()

.index

r = [1, 2, 3, 4, 5, 1, 2, 3]
print(r.index(3))

result

2

You can look up the index of a specified element by using .index (). In this case, the index is returned as 2 because it searches from the beginning (the first "3" is detected).

.index

r = [1, 2, 3, 4, 5, 1, 2, 3]
print(r.index(3, 3))

result

7

Of .index (3, 3) The first 3 specifies the element to search, such as" Search for "3" ". The trailing 3 specifies the search range, such as" Search from index "3" or later. "

◆.count()

.count

r = [1, 2, 3, 4, 5, 1, 2, 3]
print(r.count(3))

result

2

It means "count how many" 3 "are there."

◆ if statement

if

r = [1, 2, 3, 4, 5, 1, 2, 3]

if 5 in r:
    print('exist')

result

exist

If '5' exists in r, print "exist." means. The if statement will be dealt with in a later class.

◆ Arrange in numerical order

sort_and_reverse

r = [1, 2, 3, 4, 5, 1, 2, 3]

r.sort()
print(r)

r.sort(reverse=True)
print(r)

r.reverse()
print(r)

result

[1, 1, 2, 2, 3, 3, 4, 5]
[5, 4, 3, 3, 2, 2, 1, 1]
[1, 1, 2, 2, 3, 3, 4, 5]

By using .sort (), you can sort the elements of the list in ascending order of numbers. If you set .sort (reverse = True), you can do it in reverse order. There is also a method called .reverse (), so it's OK.

◆ .split () and .join ()

split_and_join

s = 'My name is Tony.'

to_split = s.split(' ')
print(to_split)

x = ' '.join(to_split)
print(x)

result

['My', 'name', 'is', 'Tony.']
My name is Tony.

By .split ('') "Use`` (space) to separate the strings and use them as elements to create a list. " It can be said. Conversely, by using ''. join (), "Put a` (space) between the elements and combine the elements into a string. " It can be said.

◆help

help

help(list)

result

class list(object)
 |  list(iterable=(), /)
 |  
 |  Built-in mutable sequence.
 |  
 |  If no argument is given, the constructor creates a new empty list.
 |  The argument must be an iterable if specified.
 |  
 |  Methods defined here:
 |  
 |  __add__(self, value, /)
 |      Return self+value.
 |  
 |  __contains__(self, key, /)
 |      Return key in self.
 |  
 |  __delitem__(self, key, /)
 |      Delete self[key].
 |  
 |  __eq__(self, value, /)
 |      Return self==value.
 |  
 |  __ge__(self, value, /)
 |      Return self>=value.
 |  
 |  __getattribute__(self, name, /)
 |      Return getattr(self, name).
 |  
 |  __getitem__(...)
 |      x.__getitem__(y) <==> x[y]
 |  
 |  __gt__(self, value, /)
 |      Return self>value.
 |  
 |  __iadd__(self, value, /)
 |      Implement self+=value.
 |  
 |  __imul__(self, value, /)
 |      Implement self*=value.
 |  
 |  __init__(self, /, *args, **kwargs)
 |      Initialize self.  See help(type(self)) for accurate signature.
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __le__(self, value, /)
 |      Return self<=value.
 |  
 |  __len__(self, /)
 |      Return len(self).
 |  
 |  __lt__(self, value, /)
 |      Return self<value.
 |  
 |  __mul__(self, value, /)
 |      Return self*value.
 |  
 |  __ne__(self, value, /)
 |      Return self!=value.
 |  
 |  __repr__(self, /)
 |      Return repr(self).
 |  
 |  __reversed__(self, /)
 |      Return a reverse iterator over the list.
 |  
 |  __rmul__(self, value, /)
 |      Return value*self.
 |  
 |  __setitem__(self, key, value, /)
 |      Set self[key] to value.
 |  
 |  __sizeof__(self, /)
 |      Return the size of the list in memory, in bytes.
 |  
 |  append(self, object, /)
 |      Append object to the end of the list.
 |  
 |  clear(self, /)
 |      Remove all items from list.
 |  
 |  copy(self, /)
 |      Return a shallow copy of the list.
 |  
 |  count(self, value, /)
 |      Return number of occurrences of value.
 |  
 |  extend(self, iterable, /)
 |      Extend list by appending elements from the iterable.
 |  
 |  index(self, value, start=0, stop=9223372036854775807, /)
 |      Return first index of value.
 |      
 |      Raises ValueError if the value is not present.
 |  
 |  insert(self, index, object, /)
 |      Insert object before index.
 |  
 |  pop(self, index=-1, /)
 |      Remove and return item at index (default last).
 |      
 |      Raises IndexError if list is empty or index is out of range.
 |  
 |  remove(self, value, /)
 |      Remove first occurrence of value.
 |      
 |      Raises ValueError if the value is not present.
 |  
 |  reverse(self, /)
 |      Reverse *IN PLACE*.
 |  
 |  sort(self, /, *, key=None, reverse=False)
 |      Stable sort *IN PLACE*.
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs) from builtins.type
 |      Create and return a new object.  See help(type) for accurate signature.
 |  
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |  
 |  __hash__ = None

You can also call how to use the method with help.