`elif`语句无法检查子字符串的字符串

编程问答 2022-08-16

问题描述

非常简短的版本：我的elif语句应该检查是否存在子字符串，它说在存在子字符串时不存在。

长版：我正在分解一个列表以提取有用的信息。由于列表是从用户派生的，因此我想检查列表是否正确填写，然后再继续。但是，当我尝试运行一些基本检查（例如是否存在正确的字符串）时，它会返回一条消息，告诉我列表项不符合我的要求。

我已经检查过，并且我的示例数据实际上已正确填写。但是，我正在努力找出我的检查失败的原因。

下面是一个复制我的问题的示例：

    #Example of a string I am turning into a list
Meta_thingys_str = "TagExampleA(omit if: Data Example 1),TagExampleA(include if: Data Example 2),TagExampleB(include if: any),TagExampleC(include if: any),TagExampleC(omit if: Data Example 3)"

#Split the string based on ',' into a list
Meta_thingys = Meta_thingys_str.split(",")

#Useful for later,to see if the list items are laid out in a manner my code can read.
obligatory_characters = (' if: ' and ')' and '(') 


#Let's loop through our "thingys"
for thingy in Meta_thingys:

    #A silly example - I have a lot more if-statements in my actual code but
    #ObvIoUsly `elif` won't run without an `if` statement.
    if ("include" in thingy) and ("any" not in thingy):
        print('yay')

    #This checks to see if the layout and characters of the list items are 
    #roughly correct
    elif (obligatory_characters not in thingy):
        print("'" + thingy + "' not recognised as a valid input (Type A Error)\n")

    #This is *supposed to* check whether either the key word 'omit' or 'include'
    #is present within each list item. Seemingly,it fails.
    elif ('omit' not in thingy) or ('include' not in thingy):
        print("\n'" + thingy + "' not recognised as a valid input (Type B Error)\n")

这将返回以下错误... 

'TagExampleA(omit if: Data Example 1)' not recognised as a valid input (Type B Error)

yay

'TagExampleB(include if: any)' not recognised as a valid input (Type B Error)


'TagExampleC(include if: any)' not recognised as a valid input (Type B Error)


'TagExampleC(omit if: Data Example 3)' not recognised as a valid input (Type B Error)

我还尝试了一个小的更改，在其中我将elif语句的条件设置为变量：

#Useful for later,to see if the list (derived from a user input) contains the
#proper information
obligatory_characters = (' if: ' and ')' and '(')
#!>>> note the change here <<<!
variable_characters = ('omit' or 'include')

#Let's loop through our "thingys"
for thingy in Meta_thingys:
#A silly example I have a lot more if-statements in my actual code
if ("include" in thingy) and ("any" not in thingy):
    print('yay')

#This checks to see if the layout and characters of the list items are
#roughly correct
elif (obligatory_characters not in thingy):
    print("'" + thingy + "' not recognised as a valid input (Type A Error)\n")

#This is *supposed to* check whether either the key word 'omit' or 'include'
#is present within each list item. Seemingly,it fails.
#!>>> and corresponding change here <<<!
elif (variable_characters not in thingy):
    print("\n'" + thingy + "' not recognised as a valid input (Type B Error)\n")

但这只是给出了稍微不同的信息... 

yay

'TagExampleB(include if: any)' not recognised as a valid input (Type B Error)


'TagExampleC(include if: any)' not recognised as a valid input (Type B Error)

解决方法

您有陈述并没有按照您认为的那样做。

elif ('omit' not in thingy) or ('include' not in thingy):

唯一不正确的方法是，如果omit和include都在thingy中，则在任何情况下都不是这样。

其他不符合您的意思的东西：

obligatory_characters = (' if: ' and ')' and '(')
print(obligatory_characters)
# '('

如果要检查字符串中是否存在几个不同的字符串，则需要执行类似的操作

must_exist = ['a','b','c']
for to_match in must_exist:
    if to_match not in search_string:
        return False
return True
for-loopif-statementpythonstringstringsubstringsubstring