how to convert string to number?

wang frank fw3 at
Wed Oct 17 00:44:00 CEST 2007

Hi, Tim,
Thanks for your help. For some reason, I only get your reply from the forum.
This is not a homework problem since I have left the school long time ago. I am new to Python and find it very interesting so I decided to try to port a big project from matlab to python. To prove the value of the python, I need to find an python way to do it. Otherwise, the result may be slower than matlab. The input file contains many lines of data starts with a label. The data lengths are not the same and the data type is mixed with int and float. Some lines start with comment sign # need to be removed from the dictionary. The mixed int and float really cause me trouble to convert the data efficiently. I will try your suggestion
I am really appreciate your help.
Frank Wang
> Date: Tue, 16 Oct 2007 13:52:31 -0500> From: python.list at> To: fw3 at> CC: python-list at> Subject: Re: how to convert string to number?> > > I have struggling to efficiently convert a string list to> > number. Here is my problem. I have a file that contains lines> > such as:> > > > data_1 1 1 2 3.5> > > > After I read the data from the file by using readlines(), each> > line contains a string. I use the re moduel to split the line> > into ['data_1', '1','1','2','3.5']. I want to create a> > dictionary which contains> > > > {'data_1':[1 1 2 3.5]}> > > > The problem is I coud not efficiently find a way to convert> > the string to number.> > > > Does anyone know how to create such dictionary efficiently?> > Despite my Spidey-sense tingling that this is a homework > assignment, as similar forms of the question have popped up > several times in the last week, I supress it this time.> > Paraphrasing Andy Dufresne, "Mr. Wang, do you trust your file?"[1]> > If you don't trust the content of your file, you have to know either> > 1) how many columns of data to expect or> 2) the type each should be (int or float)> > If the same type for each is okay, you can use something like> > >>> s = {}> >>> for line in file('in.txt'):> ... k,v = line.rstrip('\n').split(None, 1)> ... s[k] = map(float, v.split())> ...> >>> s> {'data_1': [1.0, 1.0, 2.0, 3.5], 'data_4': [1.0, 1.0, 8.0, 4.5]}> > However, if you want them to be the actual types that evaluating > them would give (thus the trust-your-source issue), you can use this:> > >>> s = {}> >>> for line in file('in.txt'):> ... k,v = line.rstrip('\n').split(None, 1)> ... s[k] = map(eval, v.split())> ...> >>> s> {'data_1': [1, 1, 2, 3.5], 'data_4': [1, 1, 8, 4.5]}> > > Both instances don't try to do anything smart with duplicate > keys, so if you want to append, Bruno Desthuilliers *just* posted > (in the last hour or so) a nice tip on this using > setdefault().append()> > -tkc> > [1]> > > > > 
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