Is there any way to format a string in Python? (Comparative introduction)

What this article brings to you is what are the methods for formatting strings in Python? (Comparative introduction) has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

% or format

1. Imperial City PK

There are currently two camps for formatting strings in Python: % and format. Which one should we choose?

Since Python 2.6 introduced the format method of formatting strings, I think % or format is not a problem at all. If you don’t believe it, look down.

# 定义一个坐标值
c = (250, 250)
# 使用%来格式化
s1 = "敌人坐标：%s" % c

The above code will obviously throw the following TypeError:

TypeError: not all arguments converted during string formatting

For this type of formatting requirement, we need to write it in the following ugly format:

# 定义一个坐标值
c = (250, 250)
# 使用%丑陋的格式化...
s1 = "敌人坐标：%s" % (c,)

Using format will not have the above problems:

# 定义一个坐标值
c = (250, 250)
# 使用format格式化
s2 = "敌人坐标：{}".format(c)

Obviously, the above One reason is enough for you to use format in future projects.

2. New features

Added f-strings in Python3.6:

In[1]: name = "djb"
In[2]: age = 18
In[3]: f"My name is {name}.I'm {age}"
Out[3]: "My name is djb.I'm 18"

Commonly used format usage

1. By position

In[1]: data = ["djb", 18]
In[2]: "Name:{0}, Age:{1}".format(*data)
Out[2]: 'Name:djb, Age:18'

2. By keyword

In[1]: data = {"name": "djb", "age": 18}
In[2]: "Name:{name}, Age:{age}".format(**data)
Out[2]: 'Name:djb, Age:18'

3. By object attribute

In[1]: class Person(object):
   ...:     def __init__(self, name, age):
   ...:         self.name = name
   ...:         self.age = age
   ...:     def __str__(self):      
   ...:         return "This guy is {self.name}, {self.age} years old.".format(self=self)
   ...:     
In[2]: p = Person("djb", 18)
In[3]: str(p)
Out[3]: 'This guy is djb, 18 years old.'

4. By subscript

In[1]: "{0[0]} is {0[1]} years old.".format(data)
Out[1]: 'djb is 18 years old.'

5. Filling and alignment

Padding is often used together with alignment

^, <, > are centered, left-aligned, and right-aligned respectively, followed by width

: Characters followed by padding can only is a character. If not specified, it will be filled with spaces by default.

In[1]: "{:>10}".format('18')
Out[1]: '        18'In[2]: "{:0>10}".format('18')
Out[2]: '0000000018'In[3]: "{:A>10}".format('18')
Out[3]: 'AAAAAAAA18

Add a zfill() method that comes with a string:

Python zfill() method returns a string of specified length. The original string is right-aligned and filled with 0s in front.

zfill() method syntax: str.zfill(width)

The parameter width specifies the length of the string. The original string is right-aligned and padded with zeros in front.

Returns a string of specified length.

In[1]: "18".zfill(10)
Out[1]: '0000000018'

6. Precision and type f

Precision is often used together with type f.

In[1]: "{:.2f}".format(3.1415926)
Out[1]: '3.14'

where .2 represents the precision of length 2, and f represents the float type.

7. Other base systems

The main ones are base systems. b, d, o, and x are binary, decimal, octal, and hexadecimal respectively.

In[1]: "{:b}".format(18)
Out[1]: '10010'In[2]: "{:d}".format(18)
Out[2]: '18'In[3]: "{:o}".format(18)
Out[3]: '22'In[4]: "{:x}".format(18)
Out[4]: '12'

8. Thousands separator

In[1]: "{:,}".format(1234567890)
Out[1]: '1,234,567,890'

Finally, to summarize, it is better to use format than % in comparison, but everyone has different usage, here is just List some advantages of format over %.

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