根据 python 中的查找模式从字符串中获取所有出现

Question

假设我有一个这样的字符串：

exp = 'CASE WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'CPU\'  THEN   \'YES\'  WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'RAM\'  THEN   \'YES\' ELSE  \'NO\' END' 

exp2 = 'CASE WHEN  ("Expressions"."ORDER_ITEMS"."QUANTITY"*"Expressions"."ORDER_ITEMS"."UNIT_PRICE")>0  THEN  ("Expressions"."ORDER_ITEMS"."QUANTITY"* "Expressions"."ORDER_ITEMS"."UNIT_PRICE") ELSE ("Expressions"."ORDER_ITEMS"."QUANTITY"+ "Expressions"."ORDER_ITEMS"."UNIT_PRICE")   END '

我想返回所有出现的 WHEN 和 THEN 以及它的文本。

这是exp1的预期output

['WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'CPU\'  THEN   \'YES\'','WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'RAM\'  THEN   \'YES\'']

这是exp2的预期output

['WHEN  ("Expressions"."ORDER_ITEMS"."QUANTITY"*"Expressions"."ORDER_ITEMS"."UNIT_PRICE")>0  THEN  ("Expressions"."ORDER_ITEMS"."QUANTITY"* "Expressions"."ORDER_ITEMS"."UNIT_PRICE")']

我试过的是这样的：

res = re.findall(r'\s*(WHEN|When|when)+\s*(.*)\s*(THEN|Then|then)+\s*')

但在我的情况下，结果列表显示了这个 output

['(WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'CPU\'  THEN   \'YES\'  WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'RAM\'  THEN)']

Answer 1

尝试：

WHEN (?:(?! +(?:WHEN|ELSE)).)* # with flags=re.I

1. WHEN - 匹配 'WHEN'
2. (?:(?? +(:.WHEN|ELSE)).) - 使用负前瞻并声明只要当前 position 不匹配后跟“WHEN”或“ELSE”的一个或多个空格字符，则再匹配一个字符。

见正则表达式演示

import re

cases = [
    'CASE WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'CPU\'  THEN   \'YES\'  WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'RAM\'  THEN   \'YES\' ELSE  \'NO\' END',
    'CASE WHEN  ("Expressions"."ORDER_ITEMS"."QUANTITY"*"Expressions"."ORDER_ITEMS"."UNIT_PRICE")>0  THEN  ("Expressions"."ORDER_ITEMS"."QUANTITY"* "Expressions"."ORDER_ITEMS"."UNIT_PRICE") ELSE ("Expressions"."ORDER_ITEMS"."QUANTITY"+ "Expressions"."ORDER_ITEMS"."UNIT_PRICE")   END '
]

for case in cases:
    res = re.findall(r'WHEN (?:(?! +(?:WHEN|ELSE)).)*', case, flags=re.I)
    print(res)

印刷：

['WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'CPU\'  THEN   \'YES\'', 'WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'RAM\'  THEN   \'YES\'']
['WHEN  ("Expressions"."ORDER_ITEMS"."QUANTITY"*"Expressions"."ORDER_ITEMS"."UNIT_PRICE")>0  THEN  ("Expressions"."ORDER_ITEMS"."QUANTITY"* "Expressions"."ORDER_ITEMS"."UNIT_PRICE")']

更新

如果要对 WHEN 和 ELSE 部分进行分组（去掉前导和尾随空格），请使用以下正则表达式：

WHEN +(.*?) +THEN +((?:(?! +(?:WHEN|ELSE)).)*)

import re

cases = [
    'CASE WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'CPU\'  THEN   \'YES\'  WHEN  "Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"=\'RAM\'  THEN   \'YES\' ELSE  \'NO\' END',
    'CASE WHEN  ("Expressions"."ORDER_ITEMS"."QUANTITY"*"Expressions"."ORDER_ITEMS"."UNIT_PRICE")>0  THEN  ("Expressions"."ORDER_ITEMS"."QUANTITY"* "Expressions"."ORDER_ITEMS"."UNIT_PRICE") ELSE ("Expressions"."ORDER_ITEMS"."QUANTITY"+ "Expressions"."ORDER_ITEMS"."UNIT_PRICE")   END '
]

for case in cases:
    results = re.findall(r'WHEN +(.*?) +THEN +((?:(?! +(?:WHEN|ELSE)).)*)', case, flags=re.I)
    for result in results:
        print(result[0], result[1])

印刷：

"Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"='CPU' 'YES'
"Expressions"."PRODUCT_CATEGORIES"."CATEGORY_NAME"='RAM' 'YES'
("Expressions"."ORDER_ITEMS"."QUANTITY"*"Expressions"."ORDER_ITEMS"."UNIT_PRICE")>0 ("Expressions"."ORDER_ITEMS"."QUANTITY"* "Expressions"."ORDER_ITEMS"."UNIT_PRICE")