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003 Help : Answers to exercises

Exercise 1

  • In a new code cell, type help(list) and look through the information provided.
help(list)

Help on class list in module builtins:

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

Exercise 2

  • Read through the help information for list, above.

  • In a new cell, create lists called alist and blist:

    alist = ['one','three','two']
blist = ['four','six','zero']

  • print the lists with:

    print(alist,blist)

Using the help information, work out how to:

  • extend alist with blist to create ['one','three','two','four','six','zero']. N.B. This is not quite the same as our use of append() above.
  • sort the new alist into alpabetical order and print the results
# ANSWERS
alist = ['one', 'three', 'two']
blist = ['four', 'six', 'zero']
print(alist, blist)

# join: 
# extend(self, iterable, /)
#      Extend list by appending elements from the iterable.
alist.extend(blist)
print("extended", alist)

# sort
# sort(self, /, *, key=None, reverse=False)
#       Stable sort *IN PLACE*.
alist.sort()
print("sorted", alist)

['one', 'three', 'two'] ['four', 'six', 'zero']
extended ['one', 'three', 'two', 'four', 'six', 'zero']
sorted ['four', 'one', 'six', 'three', 'two', 'zero']

Learning new things

Let's use that knowledge to learn something new:

Exercise 3

  • Find help for the class range to understand how to use this to generate a sequence of integers from 10 to 1 in steps of -1
  • Use what you have learned to write a for loop below that counts backwards from 10 to 0
# ANSWER
# Use what you have learned to write a 
# `for` loop below that counts backwards from 10 to 0

for i in range(10,0,-1):
    print(i)

10
9
8
7
6
5
4
3
2
1
Last update: October 8, 2020