Python Help

[Hugs12343]

Hi all

 

I am having trouble with Python v3.6. Just so you know I am using PyCharm Community Edition.

 

I want to print a concatenated output (print with text and variables).

 

My code:

print("Your final cost is $" + final_cost)

 

But it gives me an error which says: (the error is in all red though (well apart from the path to file))

 

#line 50 is the line of code above

Traceback (most recent call last):
  File "path to my file", line 50, in <module>
    print("Your fuel cost is $" + final_cost)
TypeError: must be str, not float

 

I know I can replace the plus with a comma but it puts a space between the $ and the final_cost variable which I do not want.

 

How can I output this concatenated print without this error?

 

Thanks

 

Hugs

[straight_stewie]

5 hours ago, Hugs12343 said:

How can I output this concatenated print without this error?

There are generally two ways to accomplish this, which I will outline below (I assume that your fuel cost is a float):

If it was known ahead of time that fuel_cost only had two digits after the decimal point then there would be other options we could use.
 

 

Traditional string formatting

print("Your fuel cost is $%(0:.2f)", final_cost)

 

Newer string formatting

print("Your fuel cost is ${0:.2f}", .format(final_cost))

 

 

[Guest]

To expand on the options presented by @straight_stewie

# f-string, which is only availible in 3.6 or higher
print(f"Your fuel cost is ${final_cost}")

# alternativly you could change it to a string mid line
print("Your fuel cost is $" + str(final_cost))

[Hugs12343]

10 hours ago, tjcater said:

To expand on the options presented by @straight_stewie

# f-string, which is only availible in 3.6 or higher
print(f"Your fuel cost is ${final_cost}")

# alternativly you could change it to a string mid line
print("Your fuel cost is $" + str(final_cost))

Thank-you very much. The f-string is the easiest thing to remember

[Guest]

2 hours ago, Hugs12343 said:

Thank-you very much. The f-string is the easiest thing to remember

Np, just remember to not get overly reliant on it. Its my preferred way of doing it, but there are some situations where you will need an alternative as there are several capabilities that it lacks over .format() (I tend to forget what those were as I don't run into them much, but just remember that it does lack a couple of things.)

[geo3]

Don't store money in floats or doubles. Use the decimal class. 

[straight_stewie]

6 hours ago, geo3 said:

Don't store money in floats or doubles. Use the decimal class. 

But then he couldn't skim the aggregate.

[Hugs12343]

6 hours ago, geo3 said:

Don't store money in floats or doubles. Use the decimal class. 

The easier way is to just string it at the end like this:

 

20 hours ago, tjcater said:

# alternativly you could change it to a string mid line print("Your fuel cost is $" + str(final_cost))

 

[geo3]

2 hours ago, Hugs12343 said:

The easier way is to just string it at the end like this:

 

 

No! That's wrong. Money should never be in a float or double at any point, you are going to get rounding errors. Use decimal.

[Guest]

6 hours ago, Hugs12343 said:

The easier way is to just string it at the end like this:

They weren't trying to say the method of presenting the variable is wrong, just that floating points are bad for use with money. I don't think you need to worry much unless you are dividing or working in a professional environment, but I'll further explain what they meant.

# When you define a variable this way in python, its automatically a float/double
final_value = 8.99
# The reason this can be bad is that when you work with larger values, things become inaccurate
final_value = 10 / 3
# After a certain digit numbers start to become random

# Run 1
print(final_value)
# 3.33333333333333333376546487464867948636
# Run 2
print(final_value)
# 3.33333333333333333321774386415188348748

You can see why this can be an issue, but if you are just now learning how to program, I wouldn't stress over it for now.

If you want to know more about the decimal class that was mentioned before, check out the documentation here.

Also a page for more detail about the rounding issues (Link)