# Python将字符串文字转换为浮点数 [英] Python Convert String Literal to Float

### 问题描述

I am working through the book "Introduction to Computation and Programming Using Python" by Dr. Guttag. I am working on the finger exercises for Chapter 3. I am stuck. It is section 3.2, page 25. The exercise is: Let s be a string that contains a sequence of decimal numbers separated by commas, e.g., `s = '1.23,2.4,3.123'`. Write a program that prints the sume of the numbers in s.

``````total = 0
for c in '123456789':
total += int(c)
print total.
``````

I've tried and tried but keep getting various errors. Here's my latest attempt.

``````total = 0
s = '1.23,2.4,3.123'
print s
float(s)
for c in s:
total += c
print c
print total
print 'The total should be ', 1.23+2.4+3.123
``````

### 推荐答案

Floating point values cannot have a comma. You are passing `1.23,2.4,3.123` as it is to float function, which is not valid. First split the string based on comma,

``````s = "1.23,2.4,3.123"
print s.split(",")        # ['1.23', '2.4', '3.123']
``````

Then convert each and and every element of that list to float and add them together to get the result. To feel the power of Python, this particular problem can be solved in the following ways.

``````s = "1.23,2.4,3.123"
total = sum(map(float, s.split(",")))
``````

If the number of elements is going to be too large, you can use a generator expression, like this

``````total = sum(float(item) for item in s.split(","))
``````

``````total, s = 0, "1.23,2.4,3.123"
for current_number in s.split(","):
total += float(current_number)
``````