[Tut] The Most Pythonic Way to Convert a List to a String

[Tut] The Most Pythonic Way to Convert a List to a String - Printable Version

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[Tut] The Most Pythonic Way to Convert a List to a String - xSicKxBot - 06-21-2020

The Most Pythonic Way to Convert a List to a String

To convert a list

Code:
lst

of strings to a string, use the

Code:
''.join(lst)

method with an empty separator string between the elements. If you have a list of objects, first convert each element to a string and join the result with the generator expression

Code:
''.join(str(x) for x in lst)

Problem: Given a list of elements. How to convert them to a string?

Example: Given the following list of strings.

Code:
lst = ['a', 'b', 'c']

You want to convert the list of strings to the following string:

Code:
'abc'

What’s the most Pythonic way of converting a list to a string? The answer depends on the nuances.

Here’s a quick overview before we dive into each of the methods:

https://trinket.io/embed/python/66febeb22d

Exercise: Run the code! What’s the most Pythonic way in your opinion?

Method 1: Join List of Strings

The most straightforward way is to use the

Code:
string.join(iterable)

method that concatenates all values in the

Code:
iterable

(such as a list) using the separator

Code:
string

in between the elements.

Code:
lst = ['a', 'b', 'c']
s = ''.join(lst)

The output is the following string:

Code:
print(s)
# abc

Due to its conciseness and efficiency, this is the most Pythonic way of converting a list of strings to a string. However, the join() method expects that you pass a list of strings. If you have a list of non-strings, it will throw an error!

Related article: The Ultimate Guide to Python Join

Method 2: Join List of Non-Strings with Generator Expression

So, what to do if you want to convert a list of general objects to a string?

The most Pythonic way to concatenatea list of objects is the expression

Code:
''.join(str(x) for x in lst)

that converts each object to a string using the built-in

Code:
str(...)

function in a generator expression. You can concatenate the resulting list of strings using the

Code:
join()

method on the empty string as a delimiter. The result is a single string value that’s the concatenation of the objects’ string representations.

Code:
lst = [1, 2, 3]
s = ''.join(str(x) for x in lst)
print(s)
# 123

This general method works for all objects (because all objects implement the

Code:
__str__

method per default). It’s the most Pythonic way of converting a list of non-string

Related article: What’s the most Pythonic way to join a list of objects?

Method 3: String Concatenation with +

Just for the sake of completeness, I want to highlight that you can also concatenate all strings in a list by using the + operator. If you have a list with a few objects, this is a viable option:

Code:
lst = ['a', 'b', 'c']
s = lst[0] + lst[1] + lst[2]
print(s)
# abc

This is inefficient because each

Code:
+

operator creates a new string. For

Code:
n

list elements, you create

Code:
n-1

new strings in memory.

Related article: The

Code:
+

operator for string concatenation.

This must be slightly modified when concatenating a list of objects to a single string:

Method 4: String Concatenation with + and str()

Again, if you have a list of objects, you need to convert each object to a string first:

Code:
# Method 4: String Concatenation with + and str()
lst = [1.0, 2.0, 3.0]
s = str(lst[0]) + str(lst[1]) + str(lst[2])
print(s)
# 1.02.03.0

This is very tedious and it deserves to be titled the “least Pythonic way to convert a list to a string”. You should prefer the general Method 2 that’s not only shorter and more efficient, but also more readable and generally applicable.

Method 5: Use Map + Join

The map function allows you to convert each element to a string first. You can then join the strings using the standard string.join() method on the resulting iterable of strings.

Code:
lst = [1, 2, 'hello', 3.2]
s = ''.join(map(str, lst))
print(s)
# 12hello3.2

This works beautifully for list of objects as well and it’s quite Pythonic. Many Python coders like this functional style—but I don’t consider it the most Pythonic one. Python code should be readable. Guido van Rossum, Python’s creator, tried to avoid functional programming because he didn’t find it readable compared to list comprehension or its generalization “generator expressions” (see Method 2).

Related Article: The map() function in Python

Method 6: Simple Loop

Let’s see what coders who come from another programming language such as Java would do:

Code:
lst = [1, 2, 'hello', 3.2]
s = ''
for x in lst: s += str(x)
print(s)
# 12hello3.2

They’d first create an empty string. Then, they’d add the string representation of each list element to the string until all list elements are added.

This is highly inefficient because of the repeated creation of new strings and it needs three lines instead of one. As it’s often the case in Python, you can avoid loops by using Python’s powerful built-in capabilities.

Related article:Go vs Python

Where to Go From Here?

Enough theory, let’s get some practice!

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