Problem Formulation
In the following example, you use a newline character '\n' inside the curly braces of an f-string:
my_list = ['Alice', 'Ann', 'Adam']
my_string = f'Names:\n{"\n".join(my_list)}'
print(my_string)
But if you run this code, Python raises a SyntaxError: f-string expression part cannot include a backslash. ⚡
The reason is that there is a limitation in versions of Python before 3.12 where backslashes are not allowed inside the expression portions of f-strings.
💡 Background Info: In Python 3.6 and later, f-strings offer a convenient way to format output with great flexibility. They allow you to easily incorporate variables and expressions within string literals. To create a formatted string, you can simply use an “f” or “F” prefix before the opening quotes of the string and enclose identifiers like variables in curly braces ({}).
There are multiple ways to resolve this issue.
Method 1: Using an Intermediate Variable
You can create an intermediate variable that holds the string with newlines and then use this variable inside the f-string.
my_list = ['Alice', 'Ann', 'Adam']
new_line_str = "\n".join(my_list)
my_string = f'Names:\n{new_line_str}'
print(my_string)Method 2: Using chr()
The chr() function in Python returns a string representing a character whose Unicode code point is the integer passed to the function. For example, chr(10) returns a newline character ('\n'). You can use the function inside the formatting specifier {...}.
my_list = ['Alice', 'Ann', 'Adam']
my_string = f'Names:\n{chr(10).join(my_list)}'
print(my_string)
Output:
Names: Alice Ann Adam
Method 3: Using Concatenation
Concatenate the f-string with a string that contains the newline characters.
my_list = ['Alice', 'Ann', 'Adam'] my_string = 'Names:\n' + "\n".join(my_list) print(my_string)
Method 4: Using a Function
Define a function that returns the desired string and call it inside the f-string.
my_list = ['Alice', 'Ann', 'Adam']
def get_names_string(names_list):
return "\n".join(names_list)
my_string = f'Names:\n{get_names_string(my_list)}'
print(my_string)Method 5: Using a Placeholder
Use a placeholder in the f-string and replace it with a newline character afterward. Make sure your string doesn’t already contain the placeholder or you’d mess things up.
my_list = ['Alice', 'Ann', 'Adam']
my_string = f'Names:|x|{"|x|".join(my_list)}'.replace("|x|", "\n")
print(my_string)Method 6: Using eval() Function (Not Recommended)
Although it’s possible to use eval() to evaluate a string as a Python expression, it’s generally not recommended due to security risks.
my_list = ['Alice', 'Ann', 'Adam']
s = "'\\n'.join(my_list)"
my_string = f'Names:\n{eval(s)}'
print(my_string)
The provided Python code snippet demonstrates a method to concatenate and display a list of names, each on a new line, using f-strings and the eval() function.
Initially, a list my_list is defined, containing three string elements: 'Alice', 'Ann', and 'Adam'. Subsequently, a string s is crafted, embedding a Python code expression as a string, specifically: "'\n'.join(my_list)", where "\n" represents a newline character when evaluated.
The eval() function is utilized within an f-string to evaluate s as a Python expression, effectively executing the .join() method on my_list with a newline character as the separator.
The resulting string, which concatenates "Names:\n" with the joined names, each on a new line, is stored in my_string and printed to the console, yielding an output that lists the names under the label "Names:".
Method 7: Update Your Python Version to 3.12!
I should have made this Method 1. In Python 3.12 and later, you can use backslashes inside the expression portions of f-strings, so the original example would work as expected.
⚡🧑💻 Recommended: How to Update Python?