Python调和平均计算代码抛出TypeError：只能将字符串与字符串拼接，无法拼接浮点数

Let’s work through this error and get your code running smoothly.

First, let’s break down why you’re seeing that TypeError: can only concatenate str (not "float") to str message:
When building your mensagem string, you’re trying to directly add float values (x, y, and your calculated harmonic average) to strings. Python doesn’t allow mixing string and non-string types in concatenation — it needs everything to be a string first.

Here are three straightforward ways to fix this: #

1. Explicitly convert floats to strings with str()

Wrap each float variable in str() to turn it into a string before concatenation:

mensagem = "A média harmonica de "+str(x)+" e "+str(y)+" é: "+str(média_harmonica)

2. Use f-strings (cleanest and most readable option, Python 3.6+)

F-strings let you embed variables directly in strings, and Python automatically handles type conversion for you. You can even add formatting to control decimal places for cleaner output:

# Basic version
mensagem = f"A média harmonica de {x} e {y} é: {média_harmonica}"

# With 2 decimal places for neater results
mensagem = f"A média harmonica de {x:.2f} e {y:.2f} é: {média_harmonica:.2f}"

3. Use str.format()

This is a slightly older formatting method that still works reliably:

# Basic version
mensagem = "A média harmonica de {} e {} é: {}".format(x, y, média_harmonica)

# With decimal formatting
mensagem = "A média harmonica de {:.2f} e {:.2f} é: {:.2f}".format(x, y, média_harmonica)

Bonus: Avoid overwriting your function #

One quick note — you’re assigning your calculated result to média_harmonica, which is the same name as your function. This overwrites the function, so if you tried to call média_harmonica() later in your code, it would fail. It’s better to use a distinct variable name like resultado.

Here’s the full revised code using f-strings and the improved variable name:

def média_harmonica(x,y):
    return 2/((1/x)+(1/y))

x = float(input("请输入x的数值："))
y = float(input("请输入y的数值："))
resultado = média_harmonica(x, y)
mensagem = f"A média harmonica de {x} e {y} é: {resultado}"
print(mensagem)

内容的提问来源于stack exchange，提问作者random girl