Course 1

Naming rules and conventions

命名規則與慣例

When assigning names to objects, programmers adhere to a set of rules and conventions which help to standardize code and make it more accessible to everyone. Here are some naming rules and conventions that you should know:

• Names cannot contain spaces.

• Names may be a mixture of upper and lower case characters.

• Names can’t start with a number but may contain numbers after the first character.

• Variable names and function names should be written in snake_case, which means that all letters are lowercase and words are separated using an underscore. 

• Descriptive names are better than cryptic abbreviations because they help other programmers (and you) read and interpret your code. For example, student_name is better than sn. It may feel excessive when you write it, but when you return to your code you’ll find it much easier to understand.

Common syntax errors

• Misspellings (拼寫錯誤)

• Incorrect indentations (不正確的縮排)

• Missing or incorrect key characters: (遺漏或不正確的字元)

  • Parenthetical types - ( curved ), [ square ], { curly }  括號型式 - 括號、中括號、大括號

  • Quote types - "straight-double" or 'straight-single', “curly-double” or ‘curly-single’ 引號型式

  • Block introduction characters, like colons - : 程式區塊字元

• Data type mismatches 不符合的資料類型

• Missing, incorrectly used, or misplaced Python reserved words 遺漏、不正確的使用 Python 保留字元

• Using the wrong case (uppercase/lowercase) - Python is a case-sensitive language 錯誤使用大小寫

Annotating variables by type

This has several benefits: It reduces the chance of common mistakes, helps in documenting your code for others to reuse, and allows integrated development software (IDEs) and other tools to give you better feedback.

How to annotate a variable:

a = 3                  #a is an integer
captain = "Picard"     # type: str
captain: str = “Picard”

import typing
# Define a variable of type str
z: str = "Hello, world!"
# Define a variable of type int
x: int = 10
# Define a variable of type float
y: float = 1.23
# Define a variable of type list
list_of_numbers: typing.List[int] = [1, 2, 3]
# Define a variable of type tuple
tuple_of_numbers: typing.Tuple[int, int, int] = (1, 2, 3)
# Define a variable of type dict
dictionary: typing.Dict[str, int] = {"key1": 1, "key2": 2}
# Define a variable of type set
set_of_numbers: typing.Set[int] = {1, 2, 3}

Data type conversions

Implicit vs explicit conversion 隱式 vs 顯式轉換

Implicit conversion is where the interpreter helps us out and automatically converts one data type into another, without having to explicitly tell it to do so.

Example:

# Converting integer into a float
print(7+8.5)

Explicit conversion is where we manually convert from one data type to another by calling the relevant function for the data type we want to convert to.

We used this in our video example when we wanted to print a number alongside some text. Before we could do that, we needed to call the str() function to convert the number into a string.

• str() - converts a value (often numeric) to a string data type
• int() - converts a value (usually a float) to an integer data type
• float() - converts a value (usually an integer) to a float data type

Example:

# Convert a number into a string
base = 6
height = 3
area = (base*height)/2
print("The area of the triangle is: " + str(area)) 

Operators

Arithmetic operators

• // 整數除法 (Floor division operator)
• % 餘數除法 (Modulo operator)
• ** 次方

Example for // & %

# even: 偶數
def is_even(number):
    if number % 2 == 0:
        return True
    return False
#This code has no ouput

def calculate_storage(filesize):
    block_size = 4096
    # Use floor division to calculate how many blocks are fully occupied
    full_blocks = filesize // block_size
    # Use the modulo operator to check whether there's any remainder
    partial_block_remainder = filesize % block_size
    # Depending on whether there's a remainder or not, return
    # the total number of bytes required to allocate enough blocks
    # to store your data.
    if partial_block_remainder > 0:
        return (full_blocks + 1) * block_size
    return full_blocks * block_size

print(calculate_storage(1))    # Should be 4096
print(calculate_storage(4096)) # Should be 4096
print(calculate_storage(4097)) # Should be 8192
print(calculate_storage(6000)) # Should be 8192

Comparison operators

Symbol	Name	Expression	Description
==	Equality operator	a == b	a is equal to b
!=	Not equal to operator	a != b	a is not equal to b
>	Greater than operator	a > b	a is larger than b
>=	Greater than or equal to operator	a >= b	a is larger than or equal to b
<	Less than operator	a < b	a is smaller than b
<=	Less than or equal to operator	a <= b	a is smaller than or equal to b

Good coding style

• Create a reusable function - Replace duplicate code with one reusable function to make the code easier to read and repurpose.

• Refactor code - Update code so that it is self-documenting and the intent of the code is clear.

• Add comments - Adding comments is part of creating self-documenting code. Using comments allows you to leave notes to yourself and/or other programmers to make the purpose of the code clear. 加入註解是建立自我文件化程式碼的一部分。使用註解可讓您為自己和/或其他程式設計師留下紀錄，以清楚說明程式碼的目的

Loops

While Loops

multiplier = 1
result = multiplier * 5
while result <= 50:
    print(result)
    multiplier += 1
    result = multiplier * 5
print("Done")

Common errors in Loops

• Failure to initialize variables. Make sure all the variables used in the loop’s condition are initialized before the loop.

• Unintended infinite loops. Make sure that the body of the loop modifies the variables used in the condition, so that the loop will eventually end for all possible values of the variables. You can often prevent an infinite loop by using the break keyword or by adding end criteria to the condition part of the while loop.

For Loops

friends = ['Taylor', 'Alex', 'Pat', 'Eli']
for friend in friends:
    print("Hi " + friend)

# °F to ℃
def to_celsius(x):
  return (x-32)*5/9

for x in range(0,101,10):
  print(x, to_celsius(x))

for number in range(1, 6+1, 2):
    print(number * 3)

# The loop should print 3, 9, 15

Nested for Loops

嵌入式 for 迴圈

# home_team 主隊, away_team 客隊
teams = [ 'Dragons', 'Wolves', 'Pandas', 'Unicorns']
for home_team in teams:
  for away_team in teams:
    if home_team != away_team:
      print(home_team + " vs " + away_team)

List comprehensions

列表生成式: [x for x in sequence if condition] 

# with for loop
numbers = [1, 2, 3, 4, 5]
squared_numbers = [x ** 2 for x in numbers]
print(squared_numbers)

# with for loop and if
sequence = range(10)
new_list = [x for x in sequence if x % 2 == 0]

Recursive function

遞歸函式 Use cases

1. Goes through a bunch of directories in your computer and calculates how many files are contained in each.
2. Review groups in Active Directory.

'''
def recursive_function(parameters):
    if base_case_condition(parameters):
        return base_case_value
    recursive_function(modified_parameters)
'''
def factorial(n):
  if n < 2:
    return 1
  return n * factorial(n-1)

def factorial(n):
  print("Factorial called with " + str(n))
  if n < 2:
    print("Returning 1")
    return 1
  result = n * factorial(n-1)
  print("Returning " + str(result) + " for factorial of " + str(n))
  return result

factorial(4)

Types of iterables

• String: 有順序 (sequential)、不可變 (immutable) 的文字資料的集合
• List: 有順序 (sequential)、可變 (mutable) 的任何類型資料的集合
• Dictionary: 儲存 key:value 鍵值對的資料
• Tuple: 有順序 (sequential)、不可變 (immutable) 的任何類型資料的集合
• Set: 沒有順序 (unordered)、不重複 (unique) 元素資料的集合

Resources

Naming rules and conventions

• PEP 8 – Style Guide for Python Code

Annotating variables by type

• Built-in Types — Python 3.13.0 documentation