How to print a dictionary's key?

问题:

I would like to print a specific Python dictionary key:

mydic = {}
mydic['key_name'] = 'value_name'

Now I can check if mydic.has_key('key_name'), but what I would like to do is print the name of the key 'key_name'. Of course I could use mydic.items(), but I don't want all the keys listed, merely one specific key. For instance I'd expect something like this (in pseudo-code):

print "the key name is", mydic['key_name'].name_the_key(), "and its value is", mydic['key_name']

Is there any name_the_key() method to print a key name?

---

Edit: OK, thanks a lot guys for your reactions! :) I realise my question is not well formulated and trivial. I just got confused because i realised key_name and mydic['key_name'] are two different things and i thought it would incorrect to print the key_name out of the dictionary context. But indeed i can simply use the 'key_name' to refer to the key! :)

回答1:

A dictionary has, by definition, an arbitrary number of keys. There is no "the key". You have the keys() method, which gives you a python list of all the keys, and you have the iteritems() method, which returns key-value pairs, so

for key, value in mydic.iteritems() :
    print key, value

Python 3 version:

for key, value in mydic.items() :
    print (key, value)

So you have a handle on the keys, but they only really mean sense if coupled to a value. I hope I have understood your question.

回答2:

Hmm, I think that what you might be wanting to do is print all the keys in the dictionary and their respective values?

If so you want the following:

for key in mydic:
  print "the key name is" + key + "and its value is" + mydic[key]

Make sure you use +'s instead of ,' as well. The comma will put each of those items on a separate line I think, where as plus will put them on the same line.

回答3:

Additionally you can use....

print(dictionary.items()) #prints keys and values
print(dictionary.keys()) #prints keys
print(dictionary.values()) #prints values

回答4:

dic = {"key 1":"value 1","key b":"value b"}

#print the keys:
for key in dic:
    print key

#print the values:
for value in dic.itervalues():
    print value

#print key and values
for key, value in dic.iteritems():
    print key, value

Note:In Python 3, dic.iteritems() was renamed as dic.items()

回答5:

The name of the key 'key_name' is key_name, therefore print 'key_name' or whatever variable you have representing it.

回答6:

Since we're all trying to guess what "print a key name" might mean, I'll take a stab at it. Perhaps you want a function that takes a value from the dictionary and finds the corresponding key? A reverse lookup?

def key_for_value(d, value):
    """Return a key in `d` having a value of `value`."""
    for k, v in d.iteritems():
        if v == value:
            return k

Note that many keys could have the same value, so this function will return some key having the value, perhaps not the one you intended.

If you need to do this frequently, it would make sense to construct the reverse dictionary:

d_rev = dict(v,k for k,v in d.iteritems())

回答7:

Or you can do it that manner:

for key in my_dict:
     print key, my_dict[key]

回答8:

What's wrong with using 'key_name' instead, even if it is a variable?

回答9:

import pprint
pprint.pprint(mydic.keys())

回答10:

# highlighting how to use a named variable within a string:
dict = {'a': 1, 'b': 2}

# simple method:
print "a %(a)s" % dict
print "b %(b)s" % dict

# programmatic method:
for key in dict:
    val = '%('+key+')s'
    print key, val % dict

# yields:
# a 1
# b 2

# using list comprehension
print "\n".join(["%s: %s" % (key, ('%('+key+')s') % dict) for key in dict])

# yields:
# a: 1
# b: 2

回答11:

dict = {'name' : 'Fred', 'age' : 100, 'employed' : True }

# Choose key to print (could be a user input)
x = 'name'

if x in dict.keys():
    print(x)

回答12:

Probably the quickest way to retrieve only the key name:

mydic = {}
mydic['key_name'] = 'value_name'

print mydic.items()[0][0]

Result:

key_name

Converts the dictionary into a list then it lists the first element which is the whole dict then it lists the first value of that element which is: key_name

回答13:

Make sure to do

dictionary.keys()
# rather than
dictionary.keys

回答14:

Try this:

def name_the_key(dict, key):
    return key, dict[key]

mydict = {'key1':1, 'key2':2, 'key3':3}

key_name, value = name_the_key(mydict, 'key2')
print 'KEY NAME: %s' % key_name
print 'KEY VALUE: %s' % value

回答15:

key_name = '...'
print "the key name is %s and its value is %s"%(key_name, mydic[key_name])

回答16:

If you want to get the key of a single value, the following would help:

def get_key(b): # the value is passed to the function
    for k, v in mydic.items():
        if v.lower() == b.lower():
            return k

In pythonic way:

c = next((x for x, y in mydic.items() if y.lower() == b.lower()), \
     "Enter a valid 'Value'")
print(c)

回答17:

I looked up this question, because I wanted to know how to retrieve the name of "the key" if my dictionary only had one entry. In my case, the key was unknown to me and could be any number of things. Here is what I came up with:

dict1 = {'random_word': [1,2,3]}
key_name = str([key for key in dict1]).strip("'[]'")        
print(key_name)  # equal to 'random_word', type: string.

回答18:

In Python 3:

# A simple dictionary
x = {'X':"yes", 'Y':"no", 'Z':"ok"}

# To print a specific key (for example key at index 1)
print([key for key in x.keys()][1])

# To print a specific value (for example value at index 1)
print([value for value in x.values()][1])

# To print a pair of a key with its value (for example pair at index 2)
print(([key for key in x.keys()][2], [value for value in x.values()][2]))

# To print a key and a different value (for example key at index 0 and value at index 1)
print(([key for key in x.keys()][0], [value for value in x.values()][1]))

# To print all keys and values concatenated together
print(''.join(str(key) + '' + str(value) for key, value in x.items()))

# To print all keys and values separated by commas
print(', '.join(str(key) + ', ' + str(value) for key, value in x.items()))

# To print all pairs of (key, value) one at a time
for e in range(len(x)):
    print(([key for key in x.keys()][e], [value for value in x.values()][e]))

# To print all pairs (key, value) in a tuple
print(tuple(([key for key in x.keys()][i], [value for value in x.values()][i]) for i in range(len(x))))