How to solve Python's string formatting errors?

Python is a widely used programming language, and string formatting is one of its very basic and important features. However, during the development process, sometimes we encounter some string formatting errors, which may come from various factors such as improper use of our tags and grammatical errors. This article will discuss how to solve Python string formatting errors.

1. Understand Python’s string formatting methods

In Python, there are three ways to format strings: percent sign (%) method, string.format() function method , and the new f-string method in Python3. Among them, the first two methods are the most commonly used, while f-string is a new method added in Python 3.6 version, which is relatively new.

1. Percent sign (%) method

The percent sign (%) method is the earliest and most classic string formatting method in Python. Its usage is as follows:

name = 'Tom'
age = 18
score = 95.8
print('%s is %d years old, and his score is %.1f.' % (name, age, score))

Output result:

Tom is 18 years old, and his score is 95.8.

2. String.format() function method

String.format() function method is the second string formatting method in Python , its usage is as follows:

name = 'Tom'
age = 18
score = 95.8
print('{} is {} years old, and his score is {:.1f}.'.format(name, age, score))

Output result:

Tom is 18 years old, and his score is 95.8.

3.f-string method

The Python3.6 version has added the f-string method, and the usage method is as follows :

name = 'Tom'
age = 18
score = 95.8
print(f'{name} is {age} years old, and his score is {score:.1f}.')

Output result:

Tom is 18 years old, and his score is 95.8.

2. Common Python string formatting errors and solutions

1. Marker usage errors

in In string formatting, the use of markers is very important. Common tags include %s, %d, %f, etc. Among them, %s represents a string, %d represents an integer, and %f represents a floating point number.

If we use the wrong tag, an error will occur. For example:

name = 'Tom'
age = 18
score = 95.8
print('%s is %d years old, and his score is %d.' % (name, age, score))

Output result:

TypeError: %d format: a number is required, not float

This is because score uses the %d marker, but score is a floating point number and the %f marker should be used. Therefore, we should change the code to:

name = 'Tom'
age = 18
score = 95.8
print('%s is %d years old, and his score is %.1f.' % (name, age, score))

Output result:

Tom is 18 years old, and his score is 95.8.

We can also use the string.format() function or the f-string method to avoid tag usage errors.

2. Parameter mismatch

When formatting strings, you need to ensure that the number of parameters passed matches the number of corresponding markers. If there are too many or too few parameters, an error will occur. For example:

name = 'Tom'
print('%s is %d years old.' % (name))

Output result:

TypeError: not enough arguments for format string

This is because we only passed one parameter, but there are two markers, the code should be changed to:

name = 'Tom'
age = 18
print('%s is %d years old.' % (name, age))

Output Result:

Tom is 18 years old.

3. Syntax error

Syntax error is one of the common errors in Python. Especially in string formatting, syntax errors can easily occur due to incorrect use of symbols such as brackets and quotation marks. For example:

print('My name is {}. I'm {} years old.' .format('Tom', 18))

Output result:

  File "<ipython-input-5-24fc64aa88e2>", line 1
    print('My name is {}. I'm {} years old.' .format('Tom', 18))
                            ^
SyntaxError: invalid syntax

This is because two single quotes are used in the above string, resulting in a parsing error. The code should be changed to:

print("My name is {}. I'm {} years old." .format('Tom', 18))

Output result:

My name is Tom. I'm 18 years old.

4. Summary

String formatting is a very basic and important feature in Python, master how to solve it Python string formatting errors can improve the quality of our code. When using string formatting, we need to understand Python's string formatting method and avoid common error types, such as incorrect use of markers, parameter mismatches, and syntax errors. If you encounter an error, you need to go through the code carefully to find the error and correct it.

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