Converting string number to float

[YasaminKh]

Hi,

I'm working with an xml file in python.here is the coed that i have:

import sys
from xml.dom.minidom import parse

# Load XML into tree structure                                                                                                          
tree = parse(sys.stdin)

#Find all VECTOR_AVERAGE nodes                                                                                                          
va_list = tree.getElementsByTagName('SIMULATION')[0].getElementsByTagName('AVERAGES')[0].getElementsByTagName('VECTOR_AVERAGE')

#Find the 'Density Correlations' node in the list of VECTOR_AVERAGEs                                                                    
for va in va_list:
    if va.attributes.getNamedItem('name').nodeValue == 'Density Correlations':
        density_correlations = va
        break
#Get a list of all the SCALAR_AVERAGES                                                                                                  
sa_list = density_correlations.getElementsByTagName('SCALAR_AVERAGE')

#Initialize lists for holding the data                                                                                                  
indexvalue_list = []
mean_list = []
error_list = []
variance_list = []
autocorr_list = []
newerror_list = []

#Iterate over all SCALAR_AVERAGEs and put their values into the lists                                                                   
#above.                                                                                                                                 
for sa in sa_list:
    x = sa.attributes.getNamedItem('indexvalue').nodeValue
    tuples = [eval(item) for item in x.split("--")]
    if tuples[0] == tuples[1]:
        indexvalue_list.append(tuples[0])
        #indexvalue_list.append(sa.attributes.getNamedItem('indexvalue').nodeValue)                                                     
	mean_list.append(float(sa.getElementsByTagName('MEAN')[0].childNodes[0].data))
        error_list.append(float(sa.getElementsByTagName('ERROR')[0].childNodes[0].data))
        variance_list.append(float(sa.getElementsByTagName('VARIANCE')[0].childNodes[0].data))
	autocorr_list.append(float(sa.getElementsByTagName('AUTOCORR')[0].childNodes[0].data))
        newerror_list = error_list * error_list

print "#indexvalue MEAN\tERROR\tVARIANCE\tAUTOCORR\tNewError"
for i in range(len(mean_list)):
    print "%s\t%g\t%g\t%g\t%g\t%g" % (indexvalue_list[i],mean_list[i],error_list[i],variance_list[i],autocorr_list[i],newerror_list[i])

I'm extracting data form the file and need to do some math process on them. but they apparently are not int. Cause i'm getting the following error:

newerror_list = error_list * error_list
TypeError: can't multiply sequence by non-int

Any suggestion how i can solve this problem?

[jcao219]

What you seem to be trying to do is multiply a list by another list.
What do you expect the results to be?

[YasaminKh]

I see. I want to multiply just one entery by itself.

I'm new to Python but in C++ there is this array that you can multiply like this:

array error[];

newerror = error* error ;

i need to the same thing here.

[jcao219]

Wait, just one entry?
Then do the same as in C++.

You can do this: new_error_list[i] = error[i]**2 #squared

[TrustyTony]

That would be probably then most pythonically:

new_error_list = [err*err for err in error]

err**2 is same as err*err of course if you prefer.

And in Python it is common to reuse the list and not to save result with new name (error instead of new_error_list), but sometimes it is clearer to do like above. It could be actually clearer, if you do not continue to use old error list after this operation to update error.

[YasaminKh]

I'm using it, writing like this:

for i in range(len(mean_list)):
    newerror_list[i] = error_list[i] ** 2
    print "%s\t%g\t%g\t%g\t%g\t%g" % (indexvalue_list[i],mean_list[i],error_list[i],variance_list[i],autocorr_list[i],newerror_list[i])

but it gives me this error:
File "First.py", line 43, in ?
newerror_list = error_list ** 2
IndexError: list assignment index out of range

Any idea?

[jcao219]

Change line number 2 to

newerror_list.append(error_list[i]**2)

[YasaminKh]

got it thanks. I had forgotten to initialize it.