2. Python Programming Review

Yi-Ju Tseng

Review: Introduction to Computer Science 計算機概論

Variables, Expressions, and Statements (PY4E Ch2)
Conditional Execution (PY4E Ch3)
Functions (PY4E Ch4)
Iterations (PY4E Ch5)

Variables (PY4E Ch2)

Variable Assignment

Use = to assign variables
Assignment Statements: Variable name = Value (Fix value/Constants, other variables)

Source

Variable Assignment

var1 = "test" #Assignment statement
var2, var3 = "test2","test3"
print(var1) #Print statement

test

print(var2)

test2

print(var3)

test3

print(var2+var3)

test2test3

Variable Name Rules

不可使用保留字Reserved Words
- 會變色的基本上都是保留字，如True, False等，在Python有功能的字串
只能由數字0-9、字母A-Z a-z，或是底線組成_，且不可以數字開頭
大小寫敏感
建議要是看得懂的字

True
False

False

Data Types 資料型態

文字 (text, string, character)
數值 (numeric)
布林變數 (Boolean, logic)
日期 (date)

文字 (text, string, character)

一般文字，使用單引號或雙引號標註，或是使用str(文字內容)宣告
就算內容為數字，只要使用雙引號標注，或是str宣告，即為文字型態（除非有做轉型）

text1 = "abcd"
text2 = "10"
text3 = str("xyz")
text4 = str(100)
print([text1, text2, text3,text4])

['abcd', '10', 'xyz', '100']

數值 (numeric)

包含整數 int與浮點數 float等型態。

整數 int：正數或負數，無小數點

直接指定，或是使用int(數值)宣告整數
若數值非整數，則無條件捨去
若數值是文字型態，則強迫轉型

int1 = 10
int2 = int(5)
int3 = int(6.7)
int4 = int(6.3)
int5 = int("88")
print([int1, int2, int3, int4, int5])

[10, 5, 6, 6, 88]

數值 (numeric)

包含整數 int與浮點數 float等型態。

浮點數 float：正數或負數，有小數點的數值

直接指定，或是使用float(數值)宣告整數
若數值為整數，則自動增加小數點
若數值是文字型態，則強迫轉型

float1 = float(10)
float2 = float(6.7)
float3 = float("88.8")
print([float1, float2, float3])

[10.0, 6.7, 88.8]

布林變數 (Boolean, logic)

True or False

a = 1 > 2
print(a)

False

b = 1 < 2
print(b)

True

日期 (date)

Python中並無內建的日期型態，必須使用datetime套件，使用前要記得載入（import）

!pip3 install datetime

import datetime

日期 (date)

當需要用載入套件的功能時，結構為：套件名稱.套件功能或資料類型（可能有多層）

如datetime.datetime.now()：

第一個datetime為套件名稱
第二個為套件內資料類型，有date, time, datetime等，可查閱文件
.now()為更進一步的功能（取得今日的日期物件）

today = datetime.datetime.now()
print(today)

2025-02-11 18:26:28.282649

日期 (date)

取得日期後，日期物件有許多內建的功能

如.year，.month等
可查閱文件

print(today)

2025-02-11 18:26:28.282649

print(today.year)

print(today.month)

日期 (date)

也可直接新增指定日期物件，使用方法為：

datetime.date(年,月,日)
datetime.datetime(年,月,日,時,分,秒)
時分秒不指定會直接使用預設值 (0時0分0秒)

newdate = datetime.date(2025,1,23)
print(newdate)

2025-01-23

newdatetime = datetime.datetime(2025,1,23,18,45,59)
print(newdatetime)

2025-01-23 18:45:59

newdatetime = datetime.datetime(2025,1,23)
print(newdatetime)

2025-01-23 00:00:00

Data Types 資料型態 - Recap

文字 (text, string, character)
數值 (numeric)
布林變數 (Boolean, logic)
日期 (date)

Conditional Execution (PY4E Ch3)

Operator 運算子

+加 / -減 / *乘 / /除
>大於 / <小於 / ==等於 / !=不等於
and且 / or或

+加 / -減 / *乘 / /除

int1 = 10
int2 = int(5)
print([int1, int2])

[10, 5]

Numeric Expressions

+加

int1 + int2

-減

int1 - int2

*乘

int1 * int2

/除

int1 / int2

2.0

>大於 / <小於 / ==等於 / !=不等於

int1 = 10
int2 = int(5)
print([int1, int2])

[10, 5]

>大於

int1 > int2

True

<小於

int1 < int2

False

== 等於

int1 == int2

False

!=不等於

int1 != int2

True

and / or

and且

10>5 and 10>1

True

10>5 and 1>5

False

or或

10>5 or 10>1

True

10>5 or 1>5

True

Hands-on

宣告一個文字 “15”
宣告一個數字 10
試著相加看看？是否能相加？錯誤訊息的意思是什麼？

if

x = 50
if x < 60:
    print('Slow')
if x > 80:
    print('Great')

#decrease to indicate end of block
print('Learner')

Slow
Learner

if & else if (elif)

x = 50
if x < 60:
    print('Slow')
elif x > 80:
    print('Great')

print('Learner')

Slow
Learner

if & if vs. if & else if (elif)

x = 40
if x < 50:
    print('Super Slow')
elif x < 60:
    print('Slow')

print('Learner')

Super Slow
Learner

x = 40
if x < 50:
    print('Super Slow')
if x < 60:
    print('Slow')

print('Learner')

Super Slow
Slow
Learner

if & else

x = 4
if x > 2 :
    print('Bigger')
else :
    print('Not bigger')

print('All Done')

Bigger
All Done

x = 1
if x > 2 :
    print('Bigger')
else :
    print('Not bigger')

print('All Done')

Not bigger
All Done

try except

You surround a dangerous section of code with try and except
- If the code in the try works - the except is skipped
- If the code in the try fails - it jumps to the except section

try except

astr = 'Bob'
try:
    print('Hello')
    istr = int(astr)
    print('There')
except:
    istr = -1

print('Done', istr)

Hello
Done -1

astr = '123'
try:
    print('Hello')
    istr = int(astr)
    print('There')
except:
    istr = -1

print('Done', istr)

Hello
There
Done 123

Hands-on

Write a program to convert score to the grade and print the grade according to the following criteria:

>90: A
>80 and <=90: B
>=60 and <=80: C
<60: D

Assign 76 to variable score, check the output

Conditional Execution - Recap

Operator 運算子
- + / - / * / /
- > / < / == / !=
- and / or
if
if & elif & else
try except

Function (PY4E Ch4)

Function

Stored and reused steps!

Built-in functions
- print('123'), int('123'), input()
Functions from libraries
- datetime.date(2025,1,23), from datetime library
Self-define functions

Function 函數使用

Function_name(Argument)
- print(variable or “value”)

var1 = "test"
print(var1)

test

function_name(Argument 1,Argument 2,…)
- 多個參數用,分隔

Function Definition 設計函數

We define a function using the def reserved word

def function_name(arguments):
  statement 1
  statement 2
  ...

Function Definition 設計函數

def grade(score):
  if score>90:
    print("A")
  elif score>80:
    print("B")
  elif score>=60:
    print("C")
  else:
    print("D")

this_exam = 80
grade(this_exam)

Function return value

def grade_ret(score):
  return_grade=""
  if score>90:
    return_grade="A"
  elif score>80:
    return_grade="B"
  elif score>=60:
    return_grade="C"
  else:
    return_grade="D"
  return return_grade

this_exam = 85
r_grade = grade_ret(this_exam)
print(r_grade)

Hands-on

Rewrite your pay computation with time-and-a-half for overtime and create a function called computepay which takes two parameters ( hours and rate).

Enter Hours: 45

Enter Rate: 10

Pay: 475.0 (475 = 40 * 10 + 5 * 15)

Function - Recap

Function_name(Argument)
def function name(arguments):

def function_name(arguments):
  statement 1
  statement 2
  ...

Iteration (PY4E Ch5)

Repeated Steps

Loops (repeated steps) have iteration variables that change each time through a loop.
- Often these iteration variables go through a sequence of numbers.

while

n = 5
while n > 0 :
    print(n)
    n = n - 1
print('Blastoff!')
print(n)

5
4
3
2
1
Blastoff!
0

for loop

for i in [5, 4, 3, 2, 1]:
    print(i)
print('Blastoff!')

5
4
3
2
1
Blastoff!

break

The break statement ends the current loop and jumps to the statement immediately following the loop

i = 0
while i < 5:
    if i == 3:
        break
        # Exit the loop when i is 3
    print(i)
    i += 1

0
1
2

print(0)

print(1)

print(2)

break!

continue

The continue statement ends the current iteration and jumps to the top of the loop and starts the next iteration

for i in range(5):
    if i == 3:
        continue  
        # Skip the rest of the code for i = 3
    print(i)

print(0)

print(1)

print(2)

continue!

print(4)

print(5)

Hands-on

Print the following pattern

Iteration - Recap

while
for
break
continue

2. Python Programming Review

Review: Introduction to Computer Science 計算機概論

Variables (PY4E Ch2)

Variable Assignment

Variable Assignment

Variable Name Rules

Data Types 資料型態

文字 (text, string, character)

數值 (numeric)

數值 (numeric)

布林變數 (Boolean, logic)

日期 (date)

日期 (date)

日期 (date)

日期 (date)

Data Types 資料型態 - Recap

Conditional Execution (PY4E Ch3)

Operator 運算子

+加 / -減 / *乘 / /除

>大於 / <小於 / ==等於 / !=不等於

and / or

Hands-on

if

if & else if (elif)

if & if vs. if & else if (elif)

if & else

try except

try except

Hands-on

Conditional Execution - Recap

Function (PY4E Ch4)

Function

Function 函數使用

Function Definition 設計函數

Function Definition 設計函數

Function return value

Hands-on

Function - Recap

Iteration (PY4E Ch5)

Repeated Steps

while

for loop

break

continue

Hands-on

Iteration - Recap

References

Questions?