Python：读取文件并计算总和和平均值

Question

问题是逐行读取文件，然后计算并显示文件中所有有效数字的总和和平均值。

文本文件是

contains text
79.3
56.15
67
6
text again 
57.86
6
37.863
text again 
456.675

到目前为止，这就是我所拥有的。

numbers = open('fileofnumbers.txt', 'r')

line = file_contents.readline()

numbers.close()

try:
    sum = line + line
    line = file_contents.readline()
    print "The sum of the numbers is", sum


except ValueError:
    print line

Answer 1

使用with符号可以使处理文件更加直观。

例如，将打开和关闭更改为此：

summation = 0

# Within the with block you now have access to the source variable
with open('fileofnumbers.txt', 'r') as source:
    for line in source: #iterate through all the lines of the file 
        try:
            # Since files are read in as strings, you have to cast each line to a float
            summation += float(line)
        except ValueError:
            pass

可能会让您开始

如果您想变得更聪明一点，有一个方便的python函数叫做isdigit ，它检查字符串是否都是整数值，它可以让您执行以下非常聪明的操作：

is_number = lambda number: all(number.split('.').isdigit())
answer = [float(line) for line in open('fileofnumbers.txt') if is_number(line)]

然后，求和和平均就变得微不足道了：

print sum(answer) # Sum
print sum(answer)/len(answer) #Average

Answer 2

让我们尝试使用try-except列出理解。 这可能是一个矫kill过正的方法，但肯定是一个可以放在口袋中的好工具，首先，您需要编写一个使错误消失的函数，例如http://code.activestate.com/recipes/576872-exception-handling-in-a -单行/ 。

然后，您可以像在Unix中一样通过传入argv来使用列表argv ：

intxt = """contains text
29.3423
23.1544913425
4
36.5
text again 
79.5074638
3
76.451
text again 
84.52"""

with open('in.txt','w') as fout:
    fout.write(intxt)

def safecall(f, default=None, exception=Exception):
    '''Returns modified f. When the modified f is called and throws an
    exception, the default value is returned'''
    def _safecall(*args,**argv):
        try:
            return f(*args,**argv)
        except exception:
            return default
    return _safecall

with open('in.txt','r') as fin:
    numbers = [safecall(float, 0, exception=ValueError)(i) for i in fin] 
    print "sum:", sum(numbers)
    print "avg:", sum(numbers)/float(len(numbers))

[OUT]：

sum: 336.475255142
avg: 30.5886595584