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<h1 id="programming-in-python-the-basics">Programming in Python - the basics</h1>
<h2 id="syntax-in-python">Syntax in Python</h2>
<h3 id="variables">Variables</h3>
<p><strong>Some general considerations</strong></p>
<ul>
<li>In Python, a variable is created when you first assign a value to it</li>
</ul>
<pre><code class="py">planet = 'Jupiter'
</code></pre>

<ul>
<li>The name of a variable cannot start with a digit or contain a special symbol (e.g., <code>|£$%@#</code>)</li>
<li>Some keywords cannot be used for naming variables.</li>
</ul>
<pre><code class="py">False | class | finally | is | return | None | continue | for | lambda | try | True | def
from | nonlocal | while | and | del | global | not | with | as | elif | if | or
yield | assert | else | import | pass | break | except | in | raise
</code></pre>

<ul>
<li>Python is case-sensitive: <code>planet</code> and <code>Planet</code> are different variables</li>
</ul>
<p><strong>Naming conventions</strong></p>
<p>The following naming styles are commonly distinguished:</p>
<ul>
<li>snake case: lower_case_with_underscores</li>
<li>CamelCase: CapitalizedWords</li>
<li>mixedCase: differs from CamelCase by initial lowercase character
<img src="../img/naming_convention.png">  </li>
</ul>
<p><strong>Python naming convention</strong></p>
<p>The <a href="https://peps.python.org/pep-0008/#naming-conventions" target="_blank" alt="pep-8 and Python naming conventions">Python Enhancement Proposal number 8 (PEP 8)</a> states:
<div class="note">
Function names should be lowercase, with words separated by underscores as necessary to improve readability.  Variable names follow the same convention as function names.
</div></p>
<p>Use names that make sense: <code>planet = 'Jupiter'</code> rather than <code>p = 'Jupiter'</code></p>
<h3 id="punctuation-and-indentation">Punctuation and indentation</h3>
<p>You don't need to add punctuation at the end of lines</p>
<pre><code class="py">planet = 'Jupiter'
position_from_sun = 5
</code></pre>

<p>Use semicolons in case you want to put multiple statements in a single line</p>
<pre><code class="py">planet = 'Jupiter' ; position_from_sun = 5
</code></pre>

<p>Document your code using comments</p>
<pre><code class="py"># this is the first comment
planet = 'Jupiter'  # and this is the second comment
          # ... and now a third!
text = &quot;# This is not a comment because it's inside quotes.&quot;
</code></pre>

<h3 id="data-types">Data types</h3>
<h4>Numbers</h4>
<pre><code class="py"># Integers
known_satellites = 80

# Floating point numbers
hydrogen_percentage = 0.89
</code></pre>

<p>The <code>int()</code> and <code>float()</code> methods convert booleans, numbers and number-like strings to integers and floating point numbers</p>
<pre><code class="py">known_satellites = int('80')
# 80
the_world_is_flat = float(True)
# 1.0
the_world_is_flat = float(False)
# 0.0
</code></pre>

<h4>Strings</h4>
<pre><code class="py">planet = 'Jupiter' # This is a string
</code></pre>

<p>The <code>str()</code> method returns the string representation of a given object</p>
<pre><code class="py">known_satellites = str(80)
# Use the type() function to return the type of the object
print(type(known_satellites))
# &lt;class 'str'&gt;
</code></pre>

<h4>Lists</h4>
<pre><code class="py"># You can initialise an empty list with the list() method
planets = list()
# Or using square brackets
planets = []
# To fill the list, you can put the items separated by commas between square brackets
planets = ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus']

# In Python you count from zero
print(planets[4]) # Jupiter

# To sort the list
planets_sorted_alphabetically = sorted(planets)
# planets = ['Earth', 'Jupiter', 'Mars', 'Mercury', 'Saturn', 'Uranus', 'Venus']

# Add a new item to the list
planets.append('Neptune')
# planets = ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']

# Count how many elements we have in a list
planets_count = len(planets) # 8
</code></pre>

<h3 id="string-interpolation">String interpolation</h3>
<p><em>String interpolation</em> is the process of substituting values of variables into placeholders in a string</p>
<pre><code class="py">print(&quot;The fifth planet is %s&quot; %(planets[4]))

print(&quot;The fifth planet is {}&quot;.format(planets[4]))

print(f&quot;The fifth planet is {planets[4]}&quot;)

# The fifth planet is Jupiter
</code></pre>

<h2 id="operators">Operators</h2>
<h4>Arithmetic operators</h4>
<pre><code class="py">x = 5
y = 2

# + Add two operands
print(x + y) # 7

# - Subtract the right operand from the left one
print(x - y) # 3

# * Multiply two operands
print(x * y) # 10

# / Divide the left operand by the right one. Division always returns a floating point number
print(x / y) # 2.5

# ** Raise the left operand to the power of the right one
print(x ** y) # 25

# % Return the remainder of the division. It is called modulus
print(x % y) # 1

# // Discard the fractional part of the division's result. It is called floor division
print(x // y) # 2
</code></pre>

<h4>Comparison operators</h4>
<pre><code class="py">x = 5
y = 2

# &gt; Greater than - True if the left operand is greater than the right one
print(x &gt; y) # True

# &lt; Less than - True if the left operand is less than the right one
print(x &lt; y) # False

# == Equal to - True if both operands are equal
print(x == y) # False

# != Not equal to - True if operands are not equal
print(x != y) # True

# &gt;= Greater than or equal to - True if the left operand is greater than or equal to the right one
print(x &gt;= y) # True

# &lt;= Less than or equal to - True if the left operand is less than or equal to the right one
print(x &lt;= y) # False
</code></pre>

<div class="note">
<strong>Note the difference</strong>: <code>=</code> is an assignment operator, used to assign a value to a variable. Conversely, <code>==</code> is a Boolean operator that checks whether the right operand is equal to the left one
</div>

<h4>Logic operators</h4>
<pre><code class="py">x = True
y = False

# &quot;and&quot;: True if both the operands are true
print(x and y) # False

# &quot;or&quot;: True if at least one of the operands is true
print(x or y) # True

# &quot;not&quot;: True if the operand is False and viceversa
print(not x) # False
</code></pre>

<h4>Assignment operators</h4>
<pre><code class="py"># with &quot;=&quot;
x = 5
print(x)

# with &quot;+=&quot;
x += 5 # A shortcut for x = x + 5
print(x)

# with &quot;-=&quot;
x -= 2 # A shortcut for x = x - 2
print(x)

# Try with other arithmetic operands ...
</code></pre>

<h4>Membership operators</h4>
<pre><code class="py">planets = ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus']

# &quot;in&quot;: True if value/variable is found in the sequence
print('Pluto' in planets) # False

# &quot;not in&quot;: True if value/variable is not found in the sequence
print('Moon' not in planets) # True
</code></pre>

<h2 id="conditional-statement">Conditional statement</h2>
<p>A decision might be taken only when a specific condition is satisfied</p>
<pre><code class="py">the_world_is_flat = True
if the_world_is_flat:
  print(&quot;Be careful not to fall off!&quot;)
</code></pre>

<p>Use indentation to separate <strong>code blocks</strong> by pressing the <img src="../img/tab_key.png" height="50"> key. </p>
<p>A block is a piece of Python program text that is executed as a unit, i.e., a conditional statement or a function body</p>
<h2 id="functions">Functions</h2>
<p>A block of code which defines a specific algorithm and runs only when it is called</p>
<pre><code class="py"># def {func_name}({parameter_1}, {parameter_2}, ...):
  # {func_body}
def add(num1, num2):
    return num1 + num2

my_sum = add(5,4)
print(my_sum) # 9
</code></pre>

<h2 id="exercises">Exercises</h2>
<h3 id="1st-exercise">1st Exercise</h3>
<p>The function <code>is_friend_of_harry()</code> returns a <em>True</em> value if a given name (i.e. type string) is one of the friends of Harry Potter, otherwise the function returns <em>False</em>. Let's pretend the friends of Harry Potter are: <em>"Ron", "Hermione", "Hagrid",</em> and <em>"Dumbledore"</em>.   </p>
<p><strong>Example:</strong> calling the function <code>is_friend_of_harry("Malfoy")</code> returns <em>False</em>.</p>
<p><span class="ex-part"> <strong>1.a)</strong> Define the function <code>is_friend_of_harry()</code>, and call it for each one of the following characters: <em>"Hagrid", "Voldemort",</em> and <em>"Bellatrix"</em>. Print the result (i.e. <em>True/False</em>) of each call. </span></p>
<p><button class="toggle-solution btn btn-light" onclick="toggle_click(this,'sol_1')">Show solution</button>
<div class="solution-code" id="sol_1"></p>
<pre><code class="py">def is_friend_of_harry(name):
  friends_list = [&quot;Ron&quot;, &quot;Hermione&quot;, &quot;Hagrid&quot;, &quot;Dumbledore&quot;]
  if name in friends_list:
    return True
  else:
    return False
print(is_friend_of_harry(&quot;Hagrid&quot;))
print(is_friend_of_harry(&quot;Voldemort&quot;))
print(is_friend_of_harry(&quot;Bellatrix&quot;))
</code></pre>

</div>

<p><span class="ex-part"> <strong>1.b)</strong> Write a portion of code that prints <em>"Harry has friends!"</em> if at least one of the previous characters is a friend of Harry, otherwise, print <em>"Harry has no friends!"</em>. </span></p>
<p><button class="toggle-solution btn btn-light" onclick="toggle_click(this,'sol_2')">Show solution</button>
<div class="solution-code" id="sol_2"></p>
<pre><code class="py">is_hagrid_friend = is_friend_of_harry(&quot;Hagrid&quot;)
is_voldemort_friend = is_friend_of_harry(&quot;Voldemort&quot;)
is_bellatrix_friend = is_friend_of_harry(&quot;Bellatrix&quot;)
if is_hagrid_friend or is_voldemort_friend or is_bellatrix_friend:
    print(&quot;Harry has friends!&quot;)
else:
    print(&quot;Harry has no friends!!&quot;)
</code></pre>

</div>

<p><span class="ex-part"> <strong>1.c)</strong> Let's make our function <code>is_friend_of_harry()</code> a bit more powerful. The new function should work the same way even if the given name is not well written, such that it should handle these cases:</p>
<ul>
<li>a) The letters of the name are written in different formats: uppercase and lowercase (e.g. "ron", "RON", "Ron", "roN")</li>
<li>b) The name includes spaces (e.g. "Ron  ", " Ron")</li>
<li>c) The name has both (a) and (b) cases combined in it (e.g. "   roN")</li>
</ul>
<p><strong>Hint:</strong> in python <code>{string}.lower()</code> transforms a string to its lowercase form; <code>{string}.strip()</code> removes the starting and ending whitespaces (if any); and <code>{string}.capitalize()</code> capitalizes the first letter of a string </span></p>
<p><button class="toggle-solution btn btn-light" onclick="toggle_click(this,'sol_3')">Show solution</button>
<div class="solution-code" id="sol_3"></p>
<pre><code class="py">def is_friend_of_harry(name):
  friends_list = [&quot;Ron&quot;, &quot;Hermione&quot;, &quot;Hagrid&quot;, &quot;Dumbledore&quot;]
  name = name.lower()
  name = name.strip()
  name = name.capitalize()
  if name in friends_list:
    return True
  else:
    return False
</code></pre>

</div>

<p><span class="ex-part"> <strong>1.d)</strong> Define another function <code>is_prof_friend_of_harry()</code> which returns a <em>True</em> value if a given name, which might be written in any format described (1.c), is a professor and a friend of Harry, otherwise the function must return <em>False</em>. The function should call the improved version of the function <code>is_friend_of_harry()</code> in its code (i.e. defined in (1.c)). Let's pretend the professors of Harry Potter are: <em>"Snape", "Umbridge", and "Hagrid"</em>.</span></p>
<p><button class="toggle-solution btn btn-light" onclick="toggle_click(this,'sol_4')">Show solution</button>
<div class="solution-code" id="sol_4"></p>
<pre><code class="py">def is_prof_friend_of_harry(name):
  prof_list = [&quot;Snape&quot;, &quot;Umbridge&quot;, &quot;Hagrid&quot;]
  name = name.lower()
  name = name.strip()
  name = name.capitalize()
  if name in prof_list and is_friend_of_harry(name):
    return True
  else:
    return False
print(is_prof_friend_of_harry(&quot;snape&quot;))
print(is_prof_friend_of_harry(&quot; umbridge  &quot;))
print(is_prof_friend_of_harry(&quot;  hagrid&quot;))
</code></pre>

</div>

<h3 id="2nd-exercise">2nd Exercise</h3>
<p>Each house of Hogwarts has a score which is updated with the addition or subtraction of points based on the behaviour of the houses' members, e.g. after a rule violation. We have two lists: </p>
<ul>
<li>the houses of Hogwarts <code class="py">houses = ["Gryffindor", "Hufflepuff", "Ravenclaw", "Slytherin"]</code></li>
<li>the score of each house <code class="py">scores = [0,0,0,0]</code>. The score of a house in position <em>n</em> in <code>houses</code> is placed in the same position <em>n</em> in <code>scores</code>.</li>
</ul>
<p><strong>2.a)</strong> Define the function <code>update_house_score()</code> which increments/decrements the score of a specific house with a given value of points. The function takes three parameters: <code>house_name</code>, <code>action</code>, and <code>points</code>. The value of <code>action</code> is a string which is either <em>"+"</em>(points will be added) or <em>"-"</em> (points will be subtracted)<br />
<strong>Example:</strong> Calling the function this way: <code class="py">update_house_score("Gryffindor", "+", 5)</code> should increment the score of house Gryffindor by 5 points.<br />
<strong>Hint:</strong> The function <code class="py">{list}.index({value})</code> returns the index of an element in the list, e.g. <code class="py">houses.index("Hufflepuff")</code> returns the value <em>1</em></p>
<p><button class="toggle-solution btn btn-light" onclick="toggle_click(this,'sol_5')">Show solution</button>
<div class="solution-code" id="sol_5"></p>
<pre><code class="py">houses = [&quot;Gryffindor&quot;, &quot;Hufflepuff&quot;, &quot;Ravenclaw&quot;, &quot;Slytherin&quot;]
scores = [0,0,0,0]
def update_house_score(house_name, action, points):
  house_index = houses.index(house_name)
  if action == &quot;+&quot;:
    scores[house_index] += points
  else:
    scores[house_index] -= points
</code></pre>

</div>

<p><strong>2.b)</strong> After the Quidditch cup the Houses have increased/decreased their scores: +10 Gryffindor, +7 Hufflepuff, -3 Slytherin. After the end of the game a member of house "Slytherin" helped a man riding his broom, so his house gained back 5 points. Call the function <code>update_house_score()</code> for each action in order to update the houses points and print the two lists: <code>houses</code> and <code>scores</code>.</p>
<p><button class="toggle-solution btn btn-light" onclick="toggle_click(this,'sol_6')">Show solution</button>
<div class="solution-code" id="sol_6"></p>
<pre><code class="py">update_house_score(&quot;Gryffindor&quot;, &quot;+&quot;, 10)
update_house_score(&quot;Hufflepuff&quot;, &quot;+&quot;, 7)
update_house_score(&quot;Slytherin&quot;, &quot;-&quot;, 3)
update_house_score(&quot;Slytherin&quot;, &quot;+&quot;, 5)
print(houses)
print(scores)
</code></pre>

</div>

<p><strong>2.c)</strong> redefine <code>update_house_score()</code> using the function <code>eval()</code> (<a href="https://docs.python.org/3/library/functions.html#eval">https://docs.python.org/3/library/functions.html#eval</a>)</p>
<p><button class="toggle-solution btn btn-light" onclick="toggle_click(this,'sol_2_2c')">Show solution</button>
<div class="solution-code" id="sol_2_2c"></p>
<pre><code class="py">def update_house_score(house_name, action, points):
    house_index = houses.index(house_name)
    scores[house_index] = eval(str(points) + action + str(scores[house_index]))
    return scores
</code></pre>

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                    <td>Next page</td>
                  </tr>
                  <tr>
                    <td class="prev shortcut"><kbd>p</kbd></td>
                    <td>Previous page</td>
                  </tr>
                  <tr>
                    <td class="search shortcut"><kbd>s</kbd></td>
                    <td>Search</td>
                  </tr>
                </tbody>
              </table>
            </div>
            <div class="modal-footer">
            </div>
        </div>
    </div>
</div>

    </body>
</html>