This article was compiled by reading item 4: "** Embedding in f string without using C-style format string and str.format " in " Effective Python 2nd Edition **". Thing.
There are three main methods for embedding character strings in Python.
--How to use% --How to use str.format () --How to use f string
I used it without much consciousness, but I would like to take this opportunity to think about which one is appropriate.
This is a method familiar to those who are doing Java or C language. Write as follows.
name = 'Cheese beef bowl Taro'
age = 21
print('my name is%s.%I'm d years old.' % (name, age))
output
My name is Cheese Gyudon Taro. I'm 21 years old.
Yup. Looks good. But actually, there are some problems with this method. Let's look at the following example.
name = 'Cheese beef bowl Taro'
age = 21
weight = 55.1525
print('my name is%s.%I'm d years old. Weight is about%It is dkg. From now on%Nice to meet you.' % (name, age, int(weight), name))
output
My name is Cheese Gyudon Taro. I'm 21 years old. It weighs about 55 kg. Thank you for your continued support of Cheese Gyudon Taro.
The above code has the following four problems.
-** Problem 1: If you make a mistake in the order of the types, an error will occur **
For example, if you reverse the first name and ʻage` in the above code, you will get the following error:
Traceback (most recent call last):
File "cheese.py", line 8, in <module>
print('my name is%s.%I'm d years old. Weight is about%It is dkg. From now on%Nice to meet you.' % (age, name, int(weight), name))
TypeError: %d format: a number is required, not str
The first type is an integer and the second is a character string type, so you can't reverse it. You must always be careful about the type and order.
-** Problem 2: The longer it gets, the harder it is to read **
In the above case, weight is converted to an integer, but the more complicated the formula to be assigned, the lower the readability.
"Which variable corresponds to which?"
You need to look carefully.
-** Problem 3: Need to write multiple times when using the same value **
In the above example, the same variable called name is used twice, but it is necessary to write it twice in the tuple on the right side.
-** Problem 4: Redundant using a dictionary **
Problems 1 and 3 can be solved by using dictionaries instead of tuples. You can write as follows.
name = 'Cheese beef bowl Taro'
age = 21
weight = 55.1525
print('my name is%(name)s.%(age)I'm d years old. Weight is about%(weight)It is dkg. From now on%(name)Nice to meet you.' % {'age':age, 'name':name, 'weight':int(weight)})
The output is the same.
If you write it like this, you only have to write the name that appears twice, and you don't have to worry about the order of the variables.
However, using a dictionary made it even more verbose and messy.
Next, let's see how to use str.format ().
name = 'Cheese beef bowl Taro'
age = 21
print('my name is{}is.{}歳is.'.format(name, age))
Write like this. You can also change the order of the variables by setting the index as shown below.
print('my name is{1}is.{0}歳is.'.format(age, name))
Apply to the previous example.
name = 'Cheese beef bowl Taro'
age = 21
weight = 55.1525
print('my name is{0}is.{1}歳is.体重はだいたい{2}kgis.これからも{0}Nice to meet you.'.format(age, name, int(weight)))
It seems that problems 1 and 3 above can be solved by using index.
However, although it is cleaner than the method using a dictionary with %, it is still redundant.
Finally, consider the method using the f character string. Write like this.
name = 'Cheese beef bowl Taro'
age = 21
weight = 55.1525
print(f'my name is{name}is.{age}歳is.')
Apply to the previous example
name = 'Cheese beef bowl Taro'
age = 21
weight = 55.1525
print(f'my name is{name}is.{age}歳is.体重はだいたい{int(weight)}kgis.これからも{name}Nice to meet you.')
You can see that it is much cleaner than the method using % or str.format ().
Readability is high because variables are embedded directly instead of being specified by tuples, dictionaries, or format () on the right side.
It doesn't matter which code you use, but the more complex it is, the better it is to use the f string.
--Summary of how to embed strings in Python
--The method using the f string is the most readable, so it looks good.
--By the way, note that str.format () can only be used with Python2.6 and the f string must be Python3.6 or higher.