Python - Convert Dictionary to Concatenated String

In Python, sometimes we need to convert a dictionary into a concatenated string. The keys and values of the dictionary are combined in a specific format to produce the desired string output.
For example, given the dictionary {'a': 1, 'b': 2, 'c': 3}, we may want the string "a:1, b:2, c:3". Let's discuss various methods to achieve this, starting from the most efficient to the least.

Using join() with a comprehension

We can use the join() method along with a dictionary comprehension to concatenate the dictionary into a string efficiently.

# Input dictionary
d = {'a': 1, 'b': 2, 'c': 3}

# Converting dictionary to string
s = ", ".join(f"{k}:{v}" for k, v in d.items())

# Output string
print(s)

a:1, b:2, c:3

Explanation:

• The items method retrieves all key-value pairs from the dictionary.
• A comprehension is used to format each key-value pair as key:value.
• join() method combines the formatted pairs into a single string with , as the separator.

Let's explore some more ways and see how we can convert dictionary to concatenate string.

Using for loop

We can manually concatenate the key-value pairs using a simple for loop.

# Input dictionary
d = {'a': 1, 'b': 2, 'c': 3}

# Converting dictionary to string
pairs = []
for k, v in d.items():
    pairs.append(f"{k}:{v}")
s = ", ".join(pairs)

# Output string
print(s)

a:1, b:2, c:3

Explanation:

• A for loop is used to iterate through the dictionary items.
• Each key-value pair is formatted and added to a list.
• join() method combines all elements of the list into a single string.
• This method is straightforward but less concise than using a comprehension.

Using map() with join()

map() function can be used to format each key-value pair which is then joined into a string.

# Input dictionary
d = {'a': 1, 'b': 2, 'c': 3}

# Converting dictionary to string
s = ", ".join(map(lambda x: f"{x[0]}:{x[1]}", d.items()))

# Output string
print(s)

a:1, b:2, c:3

Explanation:

• map() function applies a lambda function to each key-value pair in the dictionary.
• lambda function formats the pairs as key:value.
• join() method combines the formatted pairs into a single string.

Using reduce from functools

This method uses the reduce() function to build the concatenated string iteratively.

from functools import reduce

# Input dictionary
d = {'a': 1, 'b': 2, 'c': 3}

# Converting dictionary to string
s = reduce(lambda acc, kv: f"{acc}, {kv[0]}:{kv[1]}", d.items()).lstrip(", ")

# Output string
print(s)

('a', 1), b:2, c:3

Explanation:

• reduce() function iterates through the dictionary items, concatenating each key-value pair into a string.
• lstrip() method removes any leading , from the final string.
• This method is less efficient and less commonly used compared to others.