PYTHON-3

BY 企鵝

REVIEW

Tuple

Tuple是不可變的 (immutable)：

a = (0,1,2,3,4)
a[2] = "two" #TypeError

a = (0,1,2,3,4)

print(len(a)) #5
print(max(a)) #4
print(min(a)) #0
print(5 in a) #False
print(5 not in a) #True
print(a + a) #(0, 1, 2, 3, 4, 0, 1, 2, 3, 4)
print(a * 2) #(0, 1, 2, 3, 4, 0, 1, 2, 3, 4)

Tuple 和 List 也有很多函式是共通的：

Set

在一個 set 裡的元素必須是不可變的 (immutable)

Set Operations

x = {1, 2.33, "strings", (1, 2, 3)}

x = {1, 2, 3, 5}
x.remove(5)
print(x) #{1, 2, 3}
print(4 in x) #False
print(5 not in x) #True
x.add(6)
print(x) #{1, 2, 3, 5, 6}

y = [3, 2, 1, 5, 3, 1]
s = set(y)
print(s) #{1, 2, 3, 5}

Set

& (and)：取兩個set之間重複的部分變成一個新set

| (or)：取兩個set之間沒有重複的部分變成一個新set

^ (xor)：取兩個set之間重複以外的部分變成一個新set

x = {1, 2, 3, 5}
y = {1, 7, 8, 9}

print(x & y) #{1}
print(x | y) #{1, 2, 3, 5, 7, 8, 9}
print(x ^ y) #{2, 3, 5, 7, 8, 9}

Queue & Stack

Queue遵照First-In, First-Out (FIFO)的輸入輸出順序

Stack遵照Last-In, First-Out (LIFO)的輸入輸出順序

Queue & Stack Operations

Queue & Stack

#Queue
from queue import Queue

Q = Queue(maxsize = 3)
print(Q.qsize()) #0

Q.put('a')
Q.put('b')
Q.put('c')
print("Full :",Q.full()) #Full : True

print(Q.get()) #a
print(Q.get()) #b
print(Q.get()) #c
print("Empty :", Q.empty()) #Empty : True

Queue & Stack

#Stack
from queue import LifoQueue

st = LifoQueue(maxsize = 3)
print(st.qsize()) #0

st.put('a')
st.put('b')
st.put('c')
print("Full :", st.full()) #Full : True

print(st.get()) #c
print(st.get()) #b
print(st.get()) #a
print("Empty :", st.empty()) #Empty : True

Dictionary

字典是一種鍵(Key)-值(Value)對應的資料型態

en_to_french = {"red": "rouge", "blue": "bleu", "green": "vert"}
print(en_to_french["red"]) #rouge

STRING

String as Sequences of Characters

string(字串)，是python其中一種資料型態

string可以用類似list的方式取string當中的字元：

my_str = "Hello"
print(my_str[0]) #'H'
print(my_str[-1]) #'o'

一如list，string 也有len( )可以取得string的字元數：

my_str = "Hello"
print(len(my_str)) #5

String as Sequences of Characters

當string被宣告後，

無法更改string裡的某個字元

my_str = "Hello"
my_str[0] = 'h' #TypeError
my_str.append('t') #TypeError

String Operations

upper( )可以將所有字元都轉成大寫

lower( )則是小寫

title( )可以將字串的第一個字元轉成大寫

" " . join( )可以將一個list裡的元素接在一起，
變成一個字串，各元素以'' ''裡的內容隔開

my_str = "Hello"
print(my_str.upper()) #HELLO
print(my_str.lower()) #hello

text = "texts"
print(text.title()) #Texts

lst = ["Python", "is", "better", "than", 'C']
print(' '.join(lst)) #Python is better than C
print('::'.join(lst)) #Python::is::better::than::C
print(''.join(lst)) #PythonisbetterthanC

String Operations

split( )可以將一個字串以空白（預設）分開，

在( )放" "可以將一個字串以" "裡的內容分開

split( ,num)可以分成num+1個段落

x = "You\t\t can have tabs\t\n \t and newlines \n\n mixed in"
print(x.split())
#['You', 'can', 'have', 'tabs', 'and', 'newlines', 'mixed', 'in']

x = "Mississippi"
print(x.split("ss")) #['Mi', 'i', 'ippi']

x = 'a b c d'
print(x.split(' ', 1)) #['a', 'b c d']
print(x.split(' ', 2)) #['a', 'b', 'c d']
print(x.split(' ', 9)) #['a', 'b', 'c', 'd']

String Operations

find("string")可以在字串中尋找特定字串

rfind("string")就是從字串的最後開始往前找

count("string")計算在一個字串中該字串出現過幾次

x = "Mississippi"

print(x.find("ss")) #2
print(x.find("zz")) #-1
print(x.rfind("ss")) #5
print(x.count("ss")) #2

String Operations

startswith("string")回傳該字串是否是字串的開頭

endswith("string")回傳該字串是否是字串的結尾

如果("string", "string")，則只要其中一個成立，

就會回傳True

x = "Mississippi"
print(x.startswith("Miss")) #True
print(x.startswith("Mist")) #False
print(x.endswith("pi")) #True
print(x.endswith("p")) #False
print(x.endswith(("i", "u"))) #True

String Operations

isdigit( )會回傳字串是否只包含數字，若是則回傳True

isalpha()會回傳字串是否只包含字母，若是則回傳True

islower()會回傳字串是否只由小寫字母組成，若是則回傳True

isupper()會回傳字串是否只由大寫字母組成，若是則回傳True

x = "123"
print(x.isdigit()) #True
print(x.isalpha()) #False

x = "M"
print(x.islower()) #False
print(x.isupper()) #True

String Operations

replace("string", "string")可以將部分字串更換成指定字串

translate("string", "string")可以將指定標點符號更換成其他標點符號

( , )中前者是要被更換的字串，後者是要更換成的字串

x = "Mississippi"
x = x.replace("ss", "+++")
print(x) #Mi+++i+++ippi

x = "~x ^ (y % z)"
table = x.maketrans("~^()", "!&[]")
x = x.translate(table)
print(x) #!x & [y % z]

String Operations

在Python中，幾乎任何資料型態都可以轉換成字串

repr( )可以將其他資料型態轉為字串的型態

我們可以利用repr( )轉換進行輸出的整理：

x = [1, 2, 3]
print(type(x)) #<class 'list'>
print(type(repr(x))) #<class 'str'>

x.append([3, 4])
x.remove(2)
print("The list x is " + repr(x))
#The list x is [1, 3, [3, 4]]

Modifying Strings with List manipulations

透過資料型態間的轉換，我們也可以玩出不少花樣：

text = "Hello, World"

word_lst = list(text)
print(word_lst)
#['H', 'e', 'l', 'l', 'o', ',', ' ', 'W', 'o', 'r', 'l', 'd']

word_lst[6:] = []
print(word_lst) #['H', 'e', 'l', 'l', 'o', ',']

word_lst.reverse()
print(word_lst) #[',', 'o', 'l', 'l', 'e', 'H']

text = "-".join(word_lst)
print(text) #,-o-l-l-e-H

QUICK CHECK : STRING

my_str = "This is a string"
my_str = my_str.upper()
lst = my_str.split()
my_str = '-'.join(lst)
my_str += '!'
print(my_str) #THIS-IS-A-STRING!

lst = list(my_str)
lst.sort()
print(lst)
#['!', '-', '-', '-', 'A', 'G', 'H', 'I', 'I', 'I', 'N', 'R', 'S', 'S', 'S', 'T', 'T']
lst[0:4] = []
my_set = set(lst)
lst = list(my_set)
lst.sort()
my_str = "".join(lst)
print(my_str) #AGHINRST

請將 "This is a string" 更改成 "THIS-IS-A-STRING!"

再將 "THIS-IS-A-STRING!" 改成 "AGHINRST"

FORMAT METHOD

Format Method

Format Method (格式化輸出)，

是能夠方便串接字串和變數的方法

"{0} is {1} than {2}.".format("Python", "better", "C")
#Python is better than C.

"{{C}} is {0} than {1}.".format("better", "C++")
#{C} is better than C++.

"{a} is {b} than {c}.".format(a = "Python", b = "better", c = "C")
#Python is better than C.

"{c} is {b} than {a}.".format(a = "Python", b = "better", c = "C")
#C is better than Python.

"{c} is {b} than {a}.".format(a = "Python", b = "worse", c = "C")
#C is worse than Python.

"{0} is better than {lst[1]}.".format("Python", lst = ["C", "C++", "Java"])
#Python is better than C++.

Format Method

"{0:10} is better than C.".format("Python")
"{0:{1}} is better than C.".format("Python", 10)
"{code:{width}} is better than C.".format(code = "Python", width = 10)
#Python     is better than C.

"{0:>10} is better than C.".format("Python")
#    Python is better than C.

"{0:&>10} is better than C.".format("Python")
#&&&&Python is better than C.

format method 讓使用者能在字串中增加格式化空格：

Format Method

"{0} is {1} than {2}.".format("Python", "better", "C")
"%s is %s than %s." % ("Python", "better", "C")
#Python is better than C.

x = ["Python", "better", "C"]
"The %s contains: %s." % ("list x", x)
#The list x contains: ['Python', 'better', 'C'].

"Pi = %-6.2f" % 3.14159
#'Pi = 3.14  '

num_dict = {'e' : 2.718, "pi" : 3.14159}
"%(pi).2f - %(pi).4f - %(e).2f" % num_dict
#3.14 - 3.1416 - 2.72

除了使用上面的方法，

Python也提供類似C語言的 printf 的輸出方法

前者是字串，對應後者的tuple, int或dict

Format Method

lst = ["C", "C++", "Python"]
print(f"{lst[2]} is better than {lst[0]} and {lst[1]}.")
#Python is better than C and C++.

pi = 3.14159
print(f"pi = {pi:{10}.{2}}")
#pi =        3.1

Python 3.6以上也提供另一種formatting method：

CONTROL FLOW

Control Flow

control flow (流程控制)，

泛指條件判斷 (if-else)和迴圈 (loop)

常見迴圈有for和while兩種

提到流程控制又不得不提的就是boolean (布林值)

表示True 或 False

通常在流程控制中，會有布林值的欄位

判斷是否應該執行下列的判斷程式

Control Flow : if-elif-else

if 後面接條件式，

如果條件是回傳True就會執行，

若回傳False就不會執行（或停止執行）

electricity = 15

if electricity >= 10:
  print("so dian!!!")

Control Flow : if-elif-else

elif只會在前述所有if & elif都不成立時

才會進行判斷：

electricity = 15

if electricity > 15:
    print("electricity > 15")
elif electricity < 15:
    print("electricity < 15")
elif electricity == 15:
    print("so dian!!!")
    
#so dian!!!

Control Flow : if-elif-else

else和elif一樣只會在前述所有if & elif都不成立時

才會進行判斷：

不同的是，else不需填入條件式

當不需要執行任何動作時，可以使用pass

electricity = 3

if electricity < 5:
    pass
else:
    electricity = 5
    print(electricity)

Control Flow : for in

for 的概念是去遍歷一個複合資料結構，

for會設定一個變數，

去接遍歷的資料結構中的每個值

lst = [3, 2, 1]
for i in lst:
    print(i)
#3
#2
#1

Control Flow : for in

range(n)表示0~n的數列

讓for可以去遍歷，

並用range值取得lst中的值

lst = [1, 3, -7, 4, 9, -5, 4]
for item in range(len(lst)):
    if lst[item] < 0:
        print(lst[item])
#-7
#-5

Control Flow : range( )

range(初始值, 結束值, 間隔)

print(list(range(2, 10)))
#[2, 3, 4, 5, 6, 7, 8, 9]
print(list(range(5, 3)))
#[]
print(list(range(5, 3, -1)))
#[5, 4]
print(list(range(0, 10, 2)))
#[0, 2, 4, 6, 8]

Control Flow : for in

如果我們想因應某些條件

跳過或終止迴圈，

可以使用continue(跳過此次迴圈)

或break(跳出迴圈)

lst = [1, 3, -7, 4, 0, -5, 4]
for item in range(len(lst)):
    if lst[item] < 0:
        continue
    elif lst[item] == 0:
        break
    print(lst[item])
#1
#3
#4

Control Flow : for in

我們也可以對多重陣列進行操作：

lst = [[1, 4], [3, 7], [9, 5]]
result = 0
for item in lst:
    result += (item[0] * item[1])
print(result) #70

lst = [(1, 4), (3, 7), (9, 5)]
result = 0
for x, y in lst:
    result += (x * y)
print(result) #70

Control Flow : for in

enumerate( )，

括號裡放複合資料型態(ex:list, tuple)

會回傳(index, item)的tuple

lst = [1, 3, -7, 4, 9, -5, 4]
for i, n in enumerate(lst):
    if lst[i] < 0:
        print(n)
#-7
#-5

Control Flow : while

while迴圈的寫法如下：

while 後面接布林值，代表是否要執行此程式

如果一直是True，就會無限重覆執行

若是False，就會中斷迴圈

冒號下一行要縮排，表示在迴圈內

electricity = 15
while electricity > 10:
  print("so dian!!!")
  electricity -= 1
  
#so dian!!!
#so dian!!!
#so dian!!!
#so dian!!!
#so dian!!!

QUICK CHECK : CONTROL FLOW

1. 給定一個 list x = [1, 3, 5, 0, -1, 3, -2]，

請將所有正數取出並列印

2. 給定一個 list y = [[1, -1, 0], [2, 5, -9], [-2, -3, 0]]

請以迴圈算出所有數字相加的結果

3. 當x < -5時，列印"very low"

當 -5 <= x < 0 ，列印"low"

當x == 0時，列印"neutral"

當 0 < x <= 5 ，列印"high"

當x > 5時，列印"very high"

QUICK CHECK : CONTROL FLOW

x = [1, 3, 5, 0, -1, 3, -2]
lst = []
for i in x:
    if i > 0:
        lst.append(x[i])
print(lst) #[1, 3, 5, 0, 3]

y = [[1, -1, 0], [2, 5, -9], [-2, -3, 0]]
result = 0
for i in y:
    for j in i:
        result += j
print(result) #-7

QUICK CHECK : CONTROL FLOW

x = 9
if x < -5:
    print("very low")
elif -5 <= x < 0:
    print("low")
elif x == 0:
    print("neutral")
elif x <= 5:
    print("high")
elif x > 5:
    print("very high")

QUICK CHECK : CONTROL FLOW

infile = open("word_count.txt")
lines = infile.read().split("\n") #list

count_lines = len(lines)
count_words = 0
count_char = 0
for line in lines:
    words = line.split()
    count_words += len(words)
    count_char += len(line)

print(f"count_lines = {count_lines}, count_word = {count_words}, count_char = {count_char}")

給定一個txt檔案，

請算出該檔案有幾行、幾個單字、幾個字元

infile = open("word_count.txt")
lines = infile.read().split("\n") #list

PYTHON聯課第三堂

By d11130110周月蘅

PYTHON-3

REVIEW

STRING

FORMAT METHOD

CONTROL FLOW

PYTHON聯課第三堂

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