標籤彙整: python_built_in

Python: os.path module

os.path 模組中有幾個好用的api來取得當前檔案路徑，使得程式可以用更彈性方式去使用(避免了固定路徑)

import os

# 當前檔案的完整名稱路徑為 D:\test\test.py
# 絕對路徑
print(os.path.abspath(__file__))
# D:\test\test.py


# 檔案名稱
print(os.path.basename(__file__))
# test.py

# 上層路徑名稱
print(os.path.dirname(__file__))
# D:\test

# 檔名與副檔名
print(os.path.splitext(os.path.basename(__file__)))
# ('test', '.py')

# 承上，分別獲取並設置變數
file_name, file_ext = os.path.splitext(os.path.basename(__file__))
print(f"{file_name = }, {file_ext = }")
# file_name = 'test', file_ext = '.py'

import os

# 當前檔案的完整名稱路徑為 D:\test\test.py

# 絕對路徑

print(os.path.abspath(__file__))

# D:\test\test.py

# 檔案名稱

print(os.path.basename(__file__))

# test.py

# 上層路徑名稱

print(os.path.dirname(__file__))

# D:\test

# 檔名與副檔名

print(os.path.splitext(os.path.basename(__file__)))

# ('test', '.py')

# 承上，分別獲取並設置變數

file_name, file_ext = os.path.splitext(os.path.basename(__file__))

print(f"{file_name = }, {file_ext = }")

# file_name = 'test', file_ext = '.py'

python built-in function: abs

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abs(x, /)

回傳一個數的絕對值，引數可以是整數、浮點數或有實現 abs() 的物件。如果引數是一個複數，回傳它的純量（大小）

print(abs(-1))          # 1
print(abs(-1.3232))     # 1.3232

# 1+1.0j的純量為 (1^2 + 1^2)^1/2 => 2^1/2
print(abs(1 + 1.0j))    # 1.4142135623730951
print(abs(3 + 4.0j))    # 5.0

print(abs(-1)) # 1

print(abs(-1.3232)) # 1.3232

# 1+1.0j的純量為 (1^2 + 1^2)^1/2 => 2^1/2

print(abs(1 + 1.0j)) # 1.4142135623730951

print(abs(3 + 4.0j)) # 5.0

python built-in function: bytes

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class bytes(source=b”)
class bytes(source, encoding)
class bytes(source, encoding, errors)

bytes物件是不可變類型(bytearray則為可變類型)的序列，其元素為 0 <= x <= 256 整數

s = 'abcd'
b = bytes(s, encoding='utf-8')
print(b)       # b'abcd'
print(b[0])    # 97
print(b[:1])   # b'a'
print(b[1])    # 98
print(b[1:2])  # b'b'
print(b[1:2].decode(encoding='utf-8')) # b


for i in b:
    # 97為a在ascii編碼中10進制表示
    print(i, chr(i), bytes(chr(i), 'utf-8'))
    # 97 a b'a'
    # 98 b b'b'
    # 99 c b'c'
    # 100 d b'd'

# 產生列表
print(list(map(bytes, zip(b'abcd'))))  # [b'a', b'b', b'c', b'd']
print([i for i in b'abcd'])            # [97, 98, 99, 100]

s = 'abcd'

b = bytes(s, encoding='utf-8')

print(b) # b'abcd'

print(b[0]) # 97

print(b[:1]) # b'a'

print(b[1]) # 98

print(b[1:2]) # b'b'

print(b[1:2].decode(encoding='utf-8')) # b

for i in b:

# 97為a在ascii編碼中10進制表示

print(i, chr(i), bytes(chr(i), 'utf-8'))

# 97 a b'a'

# 98 b b'b'

# 99 c b'c'

# 100 d b'd'

# 產生列表

print(list(map(bytes, zip(b'abcd')))) # [b'a', b'b', b'c', b'd']

print([i for i in b'abcd']) # [97, 98, 99, 100]

int轉換bytes，bytes轉換回int

x = 123
v_bytes = x.to_bytes(length=4, byteorder='little', signed=False)
print(type(v_bytes), v_bytes)     # <class 'bytes'> b'{\x00\x00\x00'

v_int = int.from_bytes(v_bytes, byteorder='little', signed=False)
print(type(v_int), v_int)         # <class 'int'> 123

x = 123

v_bytes = x.to_bytes(length=4, byteorder='little', signed=False)

print(type(v_bytes), v_bytes) # <class 'bytes'> b'{\x00\x00\x00'

v_int = int.from_bytes(v_bytes, byteorder='little', signed=False)

print(type(v_int), v_int) # <class 'int'> 123

bytes類別相關方法:

# replace(bytes,bytes)
print(b'abcd'.replace(b'c', b'x'))       # b'abxd'

# find(bytes)
print(b'abcd'.find(b'c'))                # 2
print(b'abcd'.find(b'x'))                # -1


# decode()
print(b'abcd'.decode(encoding='utf-8'))  # abcd

# classmethod fromhex(string)
print(bytes.fromhex("61626364"))         # b'abc'


# hex([sep[, bytes_per_sep]])            # 61626364
print(b'abcd'.hex())

# replace(bytes,bytes)

print(b'abcd'.replace(b'c', b'x')) # b'abxd'

# find(bytes)

print(b'abcd'.find(b'c')) # 2

print(b'abcd'.find(b'x')) # -1

# decode()

print(b'abcd'.decode(encoding='utf-8')) # abcd

# classmethod fromhex(string)

print(bytes.fromhex("61626364")) # b'abc'

# hex([sep[, bytes_per_sep]]) # 61626364

print(b'abcd'.hex())

python built-in function: eval

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eval(expression, /, globals=None, locals=None)

expression: 字串
globals: 必須是一個 dictionary
locals: 可以是任何映射 (mapping) 物件

EX:

x = 1
print(eval('x + 1'))     # 2
print(eval('3 * x'))     # 3
print(eval('pow(2,2)'))  # 4

x = 3
y = 4
print(eval("x + y"))     # 7

x = 1

print(eval('x + 1')) # 2

print(eval('3 * x')) # 3

print(eval('pow(2,2)')) # 4

x = 3

y = 4

print(eval("x + y")) # 7

EX: 比較 eval 與 exec

# eval僅可以執行單個表達式, exec可執行多個表達式
# print(eval('z = 3\nprint(z + 1)'))    # SyntaxError: invalid syntax
print(exec('z = 3\nprint(z + 1)'))      # 4

# eval僅可以執行單個表達式, exec可執行多個表達式

# print(eval('z = 3\nprint(z + 1)')) # SyntaxError: invalid syntax

print(exec('z = 3\nprint(z + 1)')) # 4

EX: 動態修改PyQt

import random

d = {"A": "_01_a_rb", "B": "_02_b_rb", "C": "_03_c_rb"}

key_name = random.choice(list(d.keys()))
rb_name = d.get(key_name)

# 根據隨機選擇d中key，設置其pyqt checkbox為True(選取)
eval("self." + rb_name + ".setChecked(True)")

import random

d = {"A": "_01_a_rb", "B": "_02_b_rb", "C": "_03_c_rb"}

key_name = random.choice(list(d.keys()))

rb_name = d.get(key_name)

# 根據隨機選擇d中key，設置其pyqt checkbox為True(選取)

eval("self." + rb_name + ".setChecked(True)")

python built-in function: enumerate

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enumerate(iterable, start=0)

返回一個列舉物件，其中包含計數值與迭代資料內容
常配合 for … in 結構來處理迭代資料

seasons = ['Spring', 'Summer', 'Fall', 'Winter']
print(list(enumerate(seasons)))
# [(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]

for x, y in enumerate(seasons):
    print(x, y)

# 0 Spring
# 1 Summer
# 2 Fall
# 3 Winter

seasons = ['Spring', 'Summer', 'Fall', 'Winter']

print(list(enumerate(seasons)))

# [(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]

for x, y in enumerate(seasons):

print(x, y)

# 0 Spring

# 1 Summer

# 2 Fall

# 3 Winter

python built-in function: @classmethod

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@classmethod

運用裝飾器語法將一個方法封裝成類方法

class C:

    @classmethod
    def f(cls, arg1, arg2):  # 第一個引述為cls，非self
        pass

class C:

@classmethod

def f(cls, arg1, arg2): # 第一個引述為cls，非self

pass

類方法(classmethod)與靜態方法(static method)差異

類方法可以存取類屬性，也可實例類別對象，可用在工廠模式內加工物件
靜態方法無法訪問類或對象資料，用在輔助特定功能

EX: 類方法與靜態方法

class A:
    @classmethod
    def f1(cls, info):
        print(info)

    @staticmethod
    def f2(info):
        print(info)


class B(A):
    pass


A.f1('test')     # test
A.f2('test')     # test
B.f1('B test')   # B test

class A:

@classmethod

def f1(cls, info):

print(info)

@staticmethod

def f2(info):

print(info)

class B(A):

pass

A.f1('test') # test

A.f2('test') # test

B.f1('B test') # B test

EX: 一般方法與類方法存取類屬性

class B:

    data = 1

    @classmethod
    def f1(cls):
        print("class method")
        print(cls.data)

    def f3(self):
        self.data += 10


B.f1()         # 1

b = B()
b.f3()
print(a.data)  # 11

B.f1()         # 1，類方法存取類屬性不會被其他類物件修改

class B:

data = 1

@classmethod

def f1(cls):

print("class method")

print(cls.data)

def f3(self):

self.data += 10

B.f1() # 1

b = B()

b.f3()

print(a.data) # 11

B.f1() # 1，類方法存取類屬性不會被其他類物件修改

python built-in function: callable

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callable(object, /)

判斷object是否可呼叫，若可呼叫則回傳True
函數與類別可呼叫，若類別實作__call__函數，其實例也可以呼叫

EX: 比較函數與基本類型是否可呼叫

def f():
    return 5

print(callable(f))    # True

x = 5
print(callable(x))    # False，int不可呼叫

y = "123"
print(callable(y))    # False，str不可呼叫

def f():

return 5

print(callable(f)) # True

x = 5

print(callable(x)) # False，int不可呼叫

y = "123"

print(callable(y)) # False，str不可呼叫

EX: 類別與其實例是否可呼叫

class A:
    def __init__(self):
        pass

a = A()
print(callable(A))            # True
print(callable(a))            # False，未實現__call__，實例不可呼叫


class B:
    def __call__(self):
        print('This is B')

b = B()
print(callable(b))            # True

class A:

def __init__(self):

pass

a = A()

print(callable(A)) # True

print(callable(a)) # False，未實現__call__，實例不可呼叫

class B:

def __call__(self):

print('This is B')

b = B()

print(callable(b)) # True

python built-in function: chr

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chr(i, /)

回傳該字元的Unicode編碼位置為整數i的字串
其中i範圍限制: 0 ~ 1,114,111(0x10FFFF)

PS: ord() 與 chr() 互相轉換

# -*- coding: utf-8 -*-

# unicode編碼位置轉換成字元
for i in [65, 90, 97, 122]:
    print("%s: %s" % (i, chr(i)))
# 65: A
# 90: Z
# 97: a
# 122: z

# 字元轉換成unicode編碼位置
print(ord('a'))   # 97

# -*- coding: utf-8 -*-

# unicode編碼位置轉換成字元

for i in [65, 90, 97, 122]:

print("%s: %s" % (i, chr(i)))

# 65: A

# 90: Z

# 97: a

# 122: z

# 字元轉換成unicode編碼位置

print(ord('a')) # 97

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學習、紀錄與分析

標籤彙整: python_built_in

Python: os.path module

python built-in function: abs

python built-in function: bytes

python built-in function: eval

python built-in function: enumerate

python built-in function: @classmethod

python built-in function: callable

python built-in function: chr