Python dictionary failsafe

 

This question already has an answer here:

  • Check if a given key already exists in a dictionary 18 answers

    • You can use a try/except block: 

    try:
    # Notice that I got rid of str(Lookup)
    # raw_input always returns a string
    print Guide[Lookup]
# KeyErrors are generated when you try to access a key in a dict that doesn't exist
except KeyError:
    print 'Key not found.'

    Also, in order for your code to work, you need to make this line of code: 

    if again != ('YES' or 'Y'):

    like this: 

    if again not in ('YES', 'Y'):

    This is because, as it currently stands, your code is being evaluated by Python like so: 

    if (again != 'YES') or 'Y':

    Furthermore, since non-empty strings evaluate to True in Python, having the code like this will make the if-statement always return True because 'Y' is a non-empty string.

    Finally, you can completely get rid of this part: 

    else:
    Running = True

    since it does nothing but assign a variable to what it already equals.

    Two options.

    Use the in operator: 

    d = {}

d['foo'] = 'bar'

'foo' in d
Out[66]: True

'baz' in d
Out[67]: False

    Or use the get method of your dictionary and supply the optional default-to argument. 

    d.get('foo','OMG AN ERROR')
Out[68]: 'bar'

d.get('baz','OMG AN ERROR')
Out[69]: 'OMG AN ERROR'

    You can get what you want if you replace 

    print Guide[str(Lookup)]

    with 

    badword = 'Sorry, the word you were looking for could not be found, would you like to try another search?' 
print Guide.get(lookup,badword)

    One thing that jumped out is naming your dict with a capital letter. Generally capital letters are saved for classes. Another kind of funny thing is that this is the first time I've seen a dict actually used as a dictionary. :)

    链接地址: http://www.djcxy.com/p/28888.html

    上一篇: python2代码在使用python3.5时会出错

    下一篇: Python字典故障安全