How to print a dictionary's key?

The name of the key 'key_name' is 'key_name', therefore

print('key_name')

or whatever variable you have representing it.

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

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.

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

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())

Update for Python3: d.iteritems() is not longer supported in Python 3+ and should be replaced by d.items()

d_rev = {v: k for k, v in d.items()}

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

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

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()

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

# simple method:
print(f'a: {mapping["a"]}')
print(f'b: {mapping["b"]}')

# programmatic method:
for key, value in mapping.items():
    print(f'{key}: {value}')

# yields:
# a 1
# b 2

# using list comprehension
print('n'.join(f'{key}: {value}' for key, value in dict.items()))


# yields:
# a: 1
# b: 2

Edit: Updated for python 3’s f-strings…

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)

Or you can do it that manner:

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

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)

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

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.

Additionally you can use….

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

Make sure to do

dictionary.keys()

rather than

dictionary.keys

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))))

I’m adding this answer as one of the other answers here (https://stackoverflow.com/a/5905752/1904943) is dated (Python 2; iteritems), and the code presented — if updated for Python 3 per the suggested workaround in a comment to that answer — silently fails to return all relevant data.

Background

I have some metabolic data, represented in a graph (nodes, edges, …). In a dictionary representation of those data, keys are of the form (604, 1037, 0) (representing source and target nodes, and the edge type), with values of the form 5.3.1.9 (representing EC enzyme codes).

Find keys for given values

The following code correctly finds my keys, given values:

def k4v_edited(my_dict, value):
    values_list = []
    for k, v in my_dict.items():
        if v == value:
            values_list.append(k)
    return values_list

print(k4v_edited(edge_attributes, '5.3.1.9'))
## [(604, 1037, 0), (604, 3936, 0), (1037, 3936, 0)]

whereas this code returns only the first (of possibly several matching) keys:

def k4v(my_dict, value):
    for k, v in my_dict.items():
        if v == value:
            return k

print(k4v(edge_attributes, '5.3.1.9'))
## (604, 1037, 0)

The latter code, naively updated replacing iteritems with items, fails to return (604, 3936, 0), (1037, 3936, 0.

To access the data, you’ll need to do this:

foo = {
    "foo0": "bar0",
    "foo1": "bar1",
    "foo2": "bar2",
    "foo3": "bar3"
}
for bar in foo:
  print(bar)

Or, to access the value you just call it from the key: foo[bar]