如何调试此脚本，以便将数字替换为python中存在％的位置？

Question

What am I doing wrong?

I am trying to execute a basic code and I can't understand why the print function won't define the values with the '%' syntax. Any suggestions on what I can do to improve would be greatly appreciated. I am using Python 3.

people == 30
cars == 40
buses == 15

print ("There are %s cars on the road.") % (cars)
print ("There are %s buses outside the school.") % (buses)
print ("There are %s at the swimming pool today.") % (people)

Answer 1

Some problems in your code

• Assigment is done using the = operator, not the == operator which is used for comparison
• The formatting variable will be inside the print statement and not outside it
• You don't need to surround your variables around () to use your variables in formatting

Hence the changed code will be as follows, and note that it will work for both python2 and python3

#Use assignment operator
people = 30
cars = 40
buses = 15

#Use variables inside the print statement, which replaces the formatting operator
print("There are %s cars on the road." % cars)
print("There are %s buses outside the school." % buses)
print("There are %s at the swimming pool today." % people)

The output will be

There are 40 cars on the road.
There are 15 buses outside the school.
There are 30 at the swimming pool today.

Starting python3.7 we have a new way of formatting string using f-strings , where the variable name is replaced inside the {var}

#Use assignment operator
people = 30
cars = 40
buses = 15

#Use variables inside the f-strings
print(f"There are {cars} cars on the road.")
print(f"There are {buses} buses outside the school.")
print(f"There are {people} at the swimming pool today.")

We also have string.format to print statements, compatible for both python2 and python3 again, where the variables are replaced inside the {} in the string

#Use assignment operator
people = 30
cars = 40
buses = 15

#Use format strings
print("There are {} cars on the road.".format(cars))
print("There are {} buses outside the school.".format(cars))
print("There are {} at the swimming pool today.".format(buses))

Answer 2

In python 2.7.15 (it could be other versions honestly probably is but I use this version) if you get rid of one of the equal signs it will work. Check it out below

people = 30
cars = 40
buses = 15

print("There are %s cars on the road.") % (cars)
print("There are %s buses outside the school.") % (buses)
print("There are %s at the swimming pool today.") % (people)

In python 3 and above you can do the following method * notice the minor differences in the print statements. Where you had an extra parentheses in the print statement. Also as per the comment by @Daniel Pryden you don't need the parentheses

people = 30
cars = 40
buses = 15

print("There are %s cars on the road." % cars)
print("There are %s buses outside the school." %  buses)
print("There are %s at the swimming pool today."  %  people)

Lastly the other method as mentioned in the comments is using the .format function. The .format() function is a method of the string which class allows you to do variable substitutions and value formatting. This lets you concatenate elements together within a string through positional formatting. The definition above is from Digital Ocean the link is here

people = 30
cars = 40
buses = 15
print("There are {} cars on the road.".format(cars))
print("There are {} buses outside the school.".format(buses))
print("There are {} at the swimming pool today.".format(people))

Answer 3

As was mentioned before, the = operator is used for assignment statements . The == operator is used for value comparison expressions .

Regarding printing formatted output, in Python 3.6 or newer, the recommended approach is to use formatted string literals (aka f-strings) instead.

Putting this together, here is a corrected version for Python 3.6 or newer:

people = 10
cars = 40
buses = 15

print(f'There are {cars} cars on the road.')
print(f'There are {buses} buses outside the school.')
print(f'There are {people} at the swimming pool today.')

Answer 4

Some of typo errors I fixed:

people = 30
cars = 40
buses =15

print ("There are %s cars on the road."  %  cars)
print ("There are %s buses outside the school." %  buses)
print ("There are %s at the swimming pool today."  %  people)