473,545 Members | 1,884 Online
Bytes | Software Development & Data Engineering Community
+ Post

Home Posts Topics Members FAQ

Re: Getting a set of lambda functions

On Sun, 25 May 2008 18:46:27 -0700
John Nagle <na***@animats. comwrote:
>>func_string s=['x', 'x+1', 'x+2', 'x']
funclist = [eval('lambda x:' + func) for func in func_strings]

What are you actually trying to do, anyway? What's the
application?

You probably don't want to use "eval" that way. If you want
function objects out, use "compile".
I am writing on an application that I call pyspread
(http://pyspread.sourceforge.net).
It provides a grid (mapped to a numpy.array) into which users can type
in strings that contain python expressions.
Each expression is transformed into a function object in a second
numpy.array of the same size, so that each function can be called by
accessing the respective cell of the grid.

eval seems to work quite fine and provides nice access to globals,
system functions, modules, etc. Therefore, one can do general
programming tasks within the grid without worrying about cell
precedence.

compile returns code objects instead of function objects. I can of
course evaluate these code objects. However, when I store the code
objects, it is an extra operation each time I want to call the
function. So what is the benefit?

More specific: Is there any benefit of calling:

eval(compile(my string, '', 'eval'))

instead of

eval(mystring)

?

What are the drawbacks of my approach that I may be missing?
Any suggestions?

Best Regards

Martin
Jun 27 '08 #1
1 1644
On May 27, 1:11*am, Martin Manns <mma...@gmx.net wrote:
On Sun, 25 May 2008 18:46:27 -0700

John Nagle <na...@animats. comwrote:
>>>func_strings =['x', 'x+1', 'x+2', 'x']
>>>funclist = [eval('lambda x:' + func) for func in func_strings]
* *What are you actually trying to do, anyway? *What's the
application?
* *You probably don't want to use "eval" that way. *If you want
function objects out, use "compile".

I am writing on an application that I call pyspread
(http://pyspread.sourceforge.net).
It provides a grid (mapped to a numpy.array) into which users can type
in strings that contain python expressions.
Each expression is transformed into a function object in a second
numpy.array of the same size, so that each function can be called by
accessing the respective cell of the grid.

eval seems to work quite fine and provides nice access to globals,
system functions, modules, etc. Therefore, one can do general
programming tasks within the grid without worrying about cell
precedence.

compile returns code objects instead of function objects. I can of
course evaluate these code objects. However, when I store the code
objects, it is an extra operation each time I want to call the
function. So what is the benefit?

More specific: Is there any benefit of calling:

eval(compile(my string, '', 'eval'))

instead of

eval(mystring)

?

What are the drawbacks of my approach that I may be missing?
Any suggestions?

Best Regards

Martin
Yes, there is.
Your original example can be rewritten
>>func_string s=['x', 'x+1', 'x+2', 'x']
funclist = [compile('lambda x: %s' % func, '<string>', 'eval') for func in func_strings]
len(funclis t)
4
>>len(set(funcl ist))
3
>>eval(funcli st[0])(1)
1

Ivan
Jun 27 '08 #2

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

53
3614
by: Oliver Fromme | last post by:
Hi, I'm trying to write a Python function that parses an expression and builds a function tree from it (recursively). During parsing, lambda functions for the the terms and sub-expressions are constructed on the fly. Now my problem is lazy evaluation. Or at least I think it is. :-)
4
1510
by: Charlie Taylor | last post by:
I find that I use lambda functions mainly for callbacks to things like integration or root finding routines as follows. flow = integrate(lambda x: 2.0*pi * d(x)* v(x) * sin(a(x)),xBeg, xEnd) root = findRoot(xBeg, xEnd, lambda x: y2+ lp*(x-x2) -wallFunc( x ), tolerance=1.0E-15) I have tried using named functions instead of using lambda...
26
3446
by: Steven Bethard | last post by:
I thought it might be useful to put the recent lambda threads into perspective a bit. I was wondering what lambda gets used for in "real" code, so I grepped my Python Lib directory. Here are some of the ones I looked, classified by how I would rewrite them (if I could): * Rewritable as def statements (<name> = lambda <args>: <expr>...
4
7723
by: Paul MG | last post by:
Hi Is there a simple general way of getting the keys out of a map? Or a vector of pairs? My problem seems to be that the pair<> type returned by iterating through either has no methods to bind to to get the .first or .second elements. That seems to me to be a major oversight - so I am assuming I must be making one! For instance,...
5
2509
by: Max Rybinsky | last post by:
Hello! Please take a look at the example. >>> a = # Just a list of tuples >>> a Now i want to get a list of functions x*y/n, for each (x, y) in a:
267
10566
by: Xah Lee | last post by:
Python, Lambda, and Guido van Rossum Xah Lee, 2006-05-05 In this post, i'd like to deconstruct one of Guido's recent blog about lambda in Python. In Guido's blog written in 2006-02-10 at http://www.artima.com/weblogs/viewpost.jsp?thread=147358
23
5292
by: Kaz Kylheku | last post by:
I've been reading the recent cross-posted flamewar, and read Guido's article where he posits that embedding multi-line lambdas in expressions is an unsolvable puzzle. So for the last 15 minutes I applied myself to this problem and come up with this off-the-wall proposal for you people. Perhaps this idea has been proposed before, I don't...
21
1832
by: globalrev | last post by:
i have a rough understanding of lambda but so far only have found use for it once(in tkinter when passing lambda as an argument i could circumvent some tricky stuff). what is the point of the following function? def addn(n): return lambda x,inc=n: x+inc if i do addn(5) it returns
5
166
by: I V | last post by:
On Sun, 25 May 2008 13:43:15 +0200, Martin Manns wrote: With Ivan's approach, you lose access to the actual lambdas, so you need to create a new function and then modify its code object to actually call the code; this seems a little clunky to me. You might instead want to wrap the lambdas in an object that will do the comparison you want: ...
11
1372
by: ssecorp | last post by:
I am never redefining the or reassigning the list when using validate but since it spits the modified list back out that somehow means that the modified list is part of the environment and not the old one. i thought what happend inside a function stays inside a function meaning what comes out is independent of what comes in. Meaning if I want...
0
7478
marktang
by: marktang | last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main...
0
7668
Oralloy
by: Oralloy | last post by:
Hello folks, I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>". The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed. This is as boiled down as I can make it. ...
0
7923
jinu1996
by: jinu1996 | last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven tapestry of website design and digital marketing. It's not merely about having a website; it's about crafting an immersive digital experience that...
1
7437
by: Hystou | last post by:
Overview: Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For...
0
4960
by: conductexam | last post by:
I have .net C# application in which I am extracting data from word file and save it in database particularly. To store word all data as it is I am converting the whole word file firstly in HTML and then checking html paragraph one by one. At the time of converting from word file to html my equations which are in the word document file was convert...
0
3466
by: TSSRALBI | last post by:
Hello I'm a network technician in training and I need your help. I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs. The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols. I succeeded, with both firewalls in...
0
3448
by: adsilva | last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
1
1901
by: 6302768590 | last post by:
Hai team i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
0
722
bsmnconsultancy
by: bsmnconsultancy | last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.