Python Switch/Case 语句适配

Question

好吧，冒着因为没有“更努力”而被嘲笑的风险，我有一个场景，我一直在尝试适应 Pythonic 的 switch case 语句。我知道 python 在 3.10 中有新的 match 方法，但在我的 AWS 用例中我仅限于 3.8.10。我一直在阅读其他语言的 switch case，我想找到一种 pythonic 方法将以下混乱的 if/elif/else 语句转换为干净的 switch case。我想知道其他人在这种情况下会做什么

目标：我有一个将被传递到此代码序列中的文件名，我需要返回前三个项目（即transaction_recipient_verification、transaction_account_tokenization 等）。有时代码会收到一个包含“field_results”或“issuers”的文件名，我需要确保修剪后的返回字符串包含相应的大小写。

import random

sampleKeys = [
    'transaction_recipient_notification_status_sent/transaction_recipient_notification_status_sent_2021_10_29_12_02_14.snappy',
    'transaction_recipient_payment_status_success/transaction_recipient_payment_status_success_2021_10_29_12_02_14.snappy',
    'transaction_recipient_verification_rvdm_failure/transaction_recipient_verification_rvdm_failure_2021_10_29_12_02_14.snappy',
    'transaction_recipient_verification_rvdm_failure_field_results/transaction_recipient_verification_rvdm_failure_2021_10_29_12_02_14.snappy',
    'transaction_recipient_authentication_status_success/transaction_recipient_authentication_status_success_2021_10_29_12_02_14.snappy',
    'transaction_recipient_authentication_status_success_field_results/transaction_recipient_authentication_status_success_2021_10_29_12_02_14.snappy',
    'transaction_account_tokenization_success/transaction_account_tokenization_success_2021_10_29_12_02_14.snappy',
    'transaction_account_tokenization_success_issuers/transaction_account_tokenization_success_2021_10_29_12_02_14.snappy',
    'transaction_recipient_payment_status_terminated/transaction_recipient_payment_status_terminated_2021_10_29_12_02_14.snappy',
    'transaction_recipient_verification_rvdm_success/transaction_recipient_verification_rvdm_success_2021_10_29_12_02_14.snappy',
    'transaction_recipient_verification_rvdm_success_field_results/transaction_recipient_verification_rvdm_success_2021_10_29_12_02_14.snappy',
    'transaction_recipient_notification_status_received/transaction_recipient_notification_status_received_2021_10_29_12_02_14.snappy',
    'transaction_recipient_authentication_status_success/transaction_recipient_authentication_status_success_2021_10_29_11_17_45.snappy'
    
]

key = random.choice(sampleKeys)

array_data = any(substring in key for substring in ['_issuers', '_field_results'])
if not array_data:
    if 'transaction_recipient_notification' in key:
        keySubject = 'transaction_recipient_notification'
    elif 'transaction_recipient_authentication' in key:
        keySubject = 'transaction_recipient_authentication'
    elif 'transaction_recipient_verification' in key:
        keySubject = 'transaction_recipient_verification'
    elif 'transaction_account_verification' in key:
        keySubject = 'transaction_account_verification'
    elif 'transaction_account_tokenization' in key:
        keySubject = 'transaction_account_tokenization'
    elif 'transaction_recipient_payment' in key:
        keySubject = 'transaction_recipient_payment'
else:
    if '_issuers' in key:
        if 'transaction_recipient_notification' in key:
            keySubject = 'transaction_recipient_notification_issuers'
        elif 'transaction_recipient_authentication' in key:
            keySubject = 'transaction_recipient_authentication_issuers'
        elif 'transaction_recipient_verification' in key:
            keySubject = 'transaction_recipient_verification_issuers'
        elif 'transaction_account_verification' in key:
            keySubject = 'transaction_account_verification_issuers'
        elif 'transaction_account_tokenization' in key:
            keySubject = 'transaction_account_tokenization_issuers'
        elif 'transaction_recipient_payment' in key:
            keySubject = 'transaction_recipient_payment_issuers'
    elif '_field_results' in key:
        if 'transaction_recipient_notification' in key:
            keySubject = 'transaction_recipient_notification_field_results'
        elif 'transaction_recipient_authentication' in key:
            keySubject = 'transaction_recipient_authentication_field_results'
        elif 'transaction_recipient_verification' in key:
            keySubject = 'transaction_recipient_verification_field_results'
        elif 'transaction_account_verification' in key:
            keySubject = 'transaction_account_verification_field_results'
        elif 'transaction_account_tokenization' in key:
            keySubject = 'transaction_account_tokenization_field_results'
        elif 'transaction_recipient_payment' in key:
            keySubject = 'transaction_recipient_payment_field_results'
print(f'BEFORE ===> {key}')
print(f'AFTER  ===> {keySubject}')

可能的方向：

import re
    
class MainKeyHandleSwitch:
    
    ARRAY_OPTIONS = ['_issuers', '_field_results']
        
    def __init__(self,key):
        self._original_key = key
        self._array_data = any(substring in key for substring in self.ARRAY_OPTIONS)
        self._trimmed_dict = self.trimmed_dict()
    
    @property
    def get_trimmed_dict(self):
        return self._trimmed_dict
    
    @property
    def get_trimmed_key(self):
        return self.__get_key_subject__()
    
    def trimmed_dict(self):
        trim_dict = dict()
        trim_dict['case_one'] = re.search('transaction_recipient_notification+', self._original_key)
        trim_dict['case_two'] = re.search('transaction_recipient_authentication+', self._original_key)
        trim_dict['case_three'] = re.search('transaction_recipient_verification+', self._original_key)
        trim_dict['case_four'] = re.search('transaction_account_verification+', self._original_key)
        trim_dict['case_five'] = re.search('transaction_account_tokenization+', self._original_key)
        trim_dict['case_six'] = re.search('transaction_recipient_payment+', self._original_key)
        return trim_dict
    
    def __get_key_subject__(self):
        obj = next(item for item in list(self._trimmed_dict.values()) if item is not None)
        if not self._array_data:
            return obj.group(0)
        else:
            if '_issuers' in self._original_key:
                return f'{obj.group(0)}_issuers'
            
            elif '_field_results' in self._original_key:
                return f'{obj.group(0)}_field_results'        

以及测试类的代码：

import random

key = random.choice(sampleKeys)
print(f'before ===> {key}')
a = MainKeyHandleSwitch(key)
trimmed_key = a.get_trimmed_key
print(f'after  ===> {trimmed_key}')

Answer 1

我看到您的代码中有很多重复，所以我首先想到的是：“我可以使用循环来简化这段代码吗？”答案是肯定的！

由于您的代码重复使用了六个 subjectTypes 并且 keySubject 取决于主题类型，因此创建一个包含六个类型的列表，然后将 next() 与生成器表达式一起使用应该可以简化过度丰富的 if' s （如果没有任何相关性，则可以使用字典）。此外，您可以使用if-elif-else 子句代替array_data，以防止出现额外的块级别。

sampleKeys = [...]
key = random.choice(sampleKeys)

subjectTypes = ['transaction_recipient_notification', 'transaction_recipient_authentication',
                'transaction_recipient_verification', 'transaction_account_verification',
                'transaction_account_tokenization', 'transaction_recipient_payment']

if '_issuers' in key:
    keySubject = next(t + '_issuers' for t in subjectTypes if t in key)
elif '_field_results' in key:
    keySubject = next(t + '_field_results' for t in subjectTypes if t in key)
else:
    keySubject = next(t for t in subjectTypes if t in key)

print(f'BEFORE ===> {key}')
print(f'AFTER  ===> {keySubject}')

Answer 2

如果您正在寻找一种实现 switch 语句的方法，以下是我的解决方法：

首先像这样为开关创建一个辅助函数（我将我的放在我所有项目中使用的“myTools.py”模块中）：

def switch(v): yield lambda *c:v in c

它的工作方式是返回一个捕获开关值的函数 (lambda)，如果该值在其任何参数中，则返回 True。单个 yield 使 switch() 成为可用于 for 循环的生成器。 for 循环只会执行一次迭代，但考虑到它仍然是一个循环，它将支持 break 语句和结尾的 else 子句（当没有执行过 break 时）。

这允许以与其他语言（如 C++）中的 switch 语句非常相似的形式使用一次迭代的 for 循环：

value = 5
for case in switch(value):               # case is actually a function
    if case(0):     print("None"); break
    if case(2,4,6): print("Even"); break
    if case(3,5,7): print("Odd");  break
else:
    print("invalid value")

通过这种方法，您可以让您的 switch 函数执行任何类型的模式匹配：

def switchAllIn(v): yield lambda *c:all(s in v for s in c)

此版本的 switch 函数检查是否所有 case 参数都在 switch 值中：

value = 'The quick brown fox, jumped over the lazy dogs'

for case in switchAllIn(value):
    if case('quick','lazy'): print('oxymoron'); break
    if case('quick','fast'): print('redundant'); break
else:
    print('nothing special')

你甚至可以让它使用正则表达式：

def switchMatch(v): yield lambda *c:any(re.match(p,v) for p in c)         

value = 'The quick brown fox, jumped over the lazy dogs'
for case in switchMatch(value):
    if case(r'\bdog\b',r'\bfox\b') and not case('lazy'):
       print('lively canine')
       break
    if case(r'\bquick\b.+\bfox\b'):
       print('veloce vulpe')
       break

此解决方案具有很大的灵活性。

• 您实际上不必使用 break，因此您可以通过多个案例，甚至在 if case(...): 块之间执行一些逻辑

• 您可以将 case 与和/或运算符组合在一起，例如 if case(1) or case(3):

• 使用中断时，您可以嵌套 for case in switch 而不必为 case 函数使用不同的名称

例如：

for case in switch(letter):
    if case('a','b'):
        for case in switch(number):
            if case(1,2,3): print('vitamin'); break
            ...
        break
    if case('c','d'):
        ...
        break

• 您可以将多个 switch 调用与 zip() 结合使用

例如：

for caseL,caseN in zip(switch(L),switch(N)):
    if caseL('a','b') and caseN(1,2,3):
       print('vitamin')
       break
    ...

• 您可以使用 map() 将开关应用于列表的每个元素

在这种情况下，for循环将运行多次，您必须使用 continue 而不是 break：

L = [1,2,3,4,5]
for case in map(switch,L):
    if case(1,2,3):
       print('low')
       continue             # using continue instead of break 
    if case(4,5,6):
       print('medium')
       continue
    print('high')

但是，对于您的特定情况，switch 语句不一定是最佳解决方案。似乎有一种前缀和后缀的组合模式，其间有一组有限的关键字。您可以在由前缀、关键字和后缀组成的正则表达式上使用循环来获取 keySubject：

import re
prefixes = ('transaction_recipient_','transaction_account_')
suffixes = ('_issuers','_field_results','') # in priority order
keywords = r'notification|authentication|verification|tokenization|payment'
for suffix in suffixes:
    for prefix in prefixes:
        pattern = r'\b('+prefix+keywords+suffix+')\b'
        m = re.match(pattern,key)
        if not m: continue
        keySubject = m.group()
        break
    else: continue; break
print(f'AFTER  ===> {keySubject}')