Python String Formatting

Python String Formatting （Python字符串格式）

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Python is a popular programming language known for its simplicity, readability, and versatility. One of the essential features of Python is string formatting, which allows developers to create dynamic strings by substituting variables and expressions into placeholders within the string. In this guide, we will cover the following topics:

• What is string formatting? （-什么是字符串格式？）

• The old way of string formatting （-旧的字符串格式设置方式）

• The new way of string formatting （-字符串格式化的新方式）

• Formatting numbers （-设置数字格式）

• Formatting strings （-格式化字符串）

• Formatting dates and times （-设置日期和时间格式）

• Advanced string formatting （-高级字符串格式）

What is String Formatting? #

What is String Formatting? （什么是字符串格式？）

String formatting is the process of creating formatted strings by substituting values into placeholders within a string. In Python, there are two ways of string formatting: the old way and the new way. The old way of string formatting uses the % operator, while the new way of string formatting uses the format() method.

The Old Way of String Formatting #

The Old Way of String Formatting （旧的字符串格式）

The old way of string formatting uses the % operator to substitute values into placeholders within a string. Here’s an example:

name = "John"
age = 25
print("My name is %s and I am %d years old." % (name, age))

In this example, the %s and %d are placeholders for the name and age variables, respectively. The values of these variables are substituted into the placeholders using the % operator. （在此示例中， %s和%d分别是名称和年龄变量的占位符。使用%运算符将这些变量的值替换为占位符。）

The New Way of String Formatting #

The New Way of String Formatting （字符串格式的新方式）

The new way of string formatting uses the format() method to substitute values into placeholders within a string. Here’s an example:

name = "John"
age = 25
print("My name is {} and I am {} years old.".format(name, age))

In this example, the {} are placeholders for the name and age variables, respectively. The values of these variables are substituted into the placeholders using the format() method.

Formatting Numbers #

Formatting Numbers （设置数字格式）

Python provides various ways of formatting numbers. Here are some examples:

x = 123.456789
print("The number is {:.2f}".format(x))
print("The number is {:,}".format(x))
print("The number is {:+}".format(x))

In the first example, {:.2f} formats the number to two decimal places. In the second example, {:,} formats the number with a comma separator. In the third example, {:+} formats the number with a plus sign for positive numbers and a minus sign for negative numbers.

Formatting Strings #

Formatting Strings （设置字符串格式）

Python provides various ways of formatting strings. Here are some examples:

name = "John"
print("Hello, %s!" % name)
print("Hello, {}!".format(name))
print(f"Hello, {name}!")

In the first example, %s is a placeholder for the name variable. In the second example, {} is a placeholder for the name variable. In the third example, {name} is a placeholder for the name variable inside a f-string.

Formatting Dates and Times #

Formatting Dates and Times （设置日期和时间格式）

Python provides various ways of formatting dates and times. Here are some examples:

import datetime

date = datetime.datetime.now()
print("The date and time is {}".format(date))
print("The date and time is {: %B %d, %Y}".format(date))

In the first example, {} is a placeholder for the date variable, which is a datetime object. In the second example, {: %B %d, %Y} formats the date object to a string with the format “Month Day, Year”.

Advanced String Formatting #

Advanced String Formatting （高级字符串格式）

There are several additional techniques that Python offers to make string formatting even more flexible and powerful. （Python还提供了一些其他技术，使字符串格式更加灵活和强大。）

One such technique is using named placeholders. Instead of using positional placeholders (i.e., {}), you can use named placeholders to make your code more readable and understandable. Here’s an example:

person = {"name": "John", "age": 25}
print("My name is {name} and I am {age} years old.".format(**person))

In this example, {name} and {age} are named placeholders that correspond to the “name” and “age” keys in the person dictionary. The ** operator is used to unpack the dictionary and pass its values as keyword arguments to the format() method.

Another useful technique is using format specifiers to control the width, precision, and alignment of placeholders. Here are some examples:

x = 123.456789
print("{:<10.2f}".format(x))
print("{:,.2f}".format(x))

In the first example, {:<10.2f} formats the number to two decimal places and left-aligns it within a field of width 10. In the second example, {:,.2f} formats the number with a comma separator and two decimal places.

In addition to these techniques, Python also offers several built-in format strings that can be used to format strings, numbers, and dates/times. Here are some examples:

x = 123
print("The number is {:x}".format(x))
print("The number is {:o}".format(x))
print("The number is {:b}".format(x))
print("The number is {:e}".format(x))
print("The date and time is {:c}".format(date))

In these examples, {:x} formats the number as a hexadecimal string, {:o} formats the number as an octal string, {:b} formats the number as a binary string, {:e} formats the number in scientific notation, and {:c} formats the date/time as a character.

Conclusion #

Conclusion （结论）

In this guide, we’ve covered the basics of Python string formatting, including the old way and the new way of formatting strings, formatting numbers, formatting strings, formatting dates and times, and advanced string formatting techniques. By implementing these techniques, you can create dynamic, flexible, and powerful strings in your Python code that can help you solve complex problems and achieve your goals. （在本指南中，我们介绍了Python字符串格式化的基础知识，包括格式化字符串的旧方法和新方法、格式化数字、格式化字符串、格式化日期和时间以及高级字符串格式化技术。通过实现这些技术，您可以在Python代码中创建动态、灵活和强大的字符串，帮助您解决复杂问题并实现目标。）