CODEWITHSUNDEEP
pythonlistfunctionfor-loopappend
Srivatsan
Srivatsan

Reputation: 9363

Python append value to a list returned from a function via for loop

I have a function:

def function(x,y):
    do something
    print a,b
    return a,b

Now I use a for loop like:

for i in range(10,100,10):
    function(i,30)

which prints the values a,b for the given input values via the for loop. It also returns a,b if I say for example function(10,30) like:

Out[50]: (0.25725063633960099, 0.0039189363571677958)

I would like to append the values of a,b obtained for my different input parameters (x,y) via the for loop to two empty lists.

I tried

for i in range(10,100,10):
    list_a,list_b = function(i,30)

but list_a and list_b are still empty.

EDIT:

I have also tried:

list_a = []
list_b = []
for i in range(10,100,10):
    list_a.append(function(i,30)[0])
    list_b.append(function(i,30)[1])

But list_a and list_b are empty!

What I don't understand is that, when I call

function(10,30)[0]

for instance, it outputs a value! But why am I not able to append it to a list?

Here is the entire function as asked by a few. 

def function(N,bins):
    sample = np.log10(m200_1[n200_1>N]) # can be any 1D array
    mean,scatter = stats.norm.fit(sample) #Gives the paramters of the fit to the histogram
    err_std = scatter/np.sqrt(len(sample))

    if N<30:
        x_fit = np.linspace(sample.min(),sample.max(),100)
        pdf_fitted = stats.norm.pdf(x_fit,loc=mean,scale=scatter) #Gives the PDF, given the parameters from norm.fit
        print "scatter for N>%s is %s" %(N,scatter)
        print "error on scatter for N>%s is %s" %(N,err_std)
        print "mean for N>%s is %s" %(N,mean)  

    else:
        x_fit = np.linspace(sample.min(),sample.max(),100)
        pdf_fitted = stats.norm.pdf(x_fit,loc=mean,scale=scatter) #Gives the PDF, given the parameters from norm.fit
        print "scatter for N>%s is %s" %(N,scatter) 
        print "error on scatter for N>%s is %s" %(N,err_std)
        print "mean for N>%s is %s" %(N,mean)

    return scatter,err_std

Upvotes: 0

Views: 8178

Answers (4)

Salvatore
Salvatore

Reputation: 46

Something like this should work:

# Define a simple test function
def function_test(x,y): 
    return x,y

# Initialize two empty lists
list_a = []
list_b = []
# Loop over a range
for i in range(10,100,10):
        a = function_test(i,30) # The output of the function is a tuple, which we put in "a"
        # Append the output of the function to the lists
        # We access each element of the output tuple "a" via indices
        list_a.append(a[0])
        list_b.append(a[1])
# Print the final lists      
print(list_a)
print(list_b)

Upvotes: 1

PhilChang
PhilChang

Reputation: 2691

you can use list comprehension first, get list_a, list_b via zip.

def function(x,y):
    return x,y

result = [function(i,30) for i in range(10,100,10)]
list_a, list_b = zip(*result)

Upvotes: 5

Hao Wang
Hao Wang

Reputation: 43

you may need to try map() function, which is more friendly~~

Understanding the map function

which should be the same as in python 3: def map(func, iterable): for i in iterable: yield func(i)

under python 2 map will return the full list

Upvotes: -2

turkus
turkus

Reputation: 4893

You mean something like that:

list_a = []
list_b = []

for i in range(10,100,10):
    a, b = function(i,30)
    list_a.append(a)
    list_b.append(b)

Upvotes: 0

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