How to Insert a Variable into a String in Python?

How to Interpolate a Variable into a String in Python

When working with Python strings, it's often necessary to include the value of a variable within the string. This is known as string interpolation.

The Problem:

Consider the following code:

num = 40
plot.savefig('hanning40.pdf') # This line is problematic

Here, we want to save the plot using a file name that includes the value of num. However, simply inserting the variable like this doesn't work.

The Solution:

There are several methods to interpolate a variable into a string in Python:

1. f-strings:

plot.savefig(f'hanning{num}.pdf')

This method uses f-strings, which were introduced in Python 3.6. It's the preferred and most concise way to interpolate variables.

2. str.format():

plot.savefig('hanning{0}.pdf'.format(num))

This method uses the format() method of the string class. The {} placeholder represents the position of the variable in the format string.

3. String Concatenation:

plot.savefig('hanning' + str(num) + '.pdf')

This method involves concatenating the string with the string representation of the variable. However, it's not as efficient or readable as the other methods.

4. Conversion Specifier:

plot.savefig('hanning%s.pdf' % num)

This method uses a conversion specifier (%s) to represent the variable. It's similar to string concatenation but uses a more compact syntax.

5. Local Variable Names (Neat Trick):

plot.savefig('hanning%(num)s.pdf' % locals())

This trick involves passing the local variable dictionary to the format string. It allows you to use the variable name as a placeholder within the string.

6. string.Template:

plot.savefig(string.Template('hanning${num}.pdf').substitute(locals()))

This method uses the string.Template class to interpolate variables. It offers advanced formatting options, but it's less commonly used than the other methods.

Additional Notes:

• When interpolating integers into strings, using str() to convert them to strings is recommended for clarity and type safety.
• For more details on string interpolation in Python, refer to the Python documentation or external resources such as the references provided.

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