CODEWITHSUNDEEP
pythonpython-3.xlistlist-comprehension
Luismaia1994
Luismaia1994

Reputation: 143

Variable p referenced before assignment in enclosing scope

I'm trying to solve a problem I already solved before but now using list comprehensions. The problem is simple I have a list and I want to invert it using list comprehension

Defining the first list was easy but when I append the inverted list it gives me the error in the title. I know we should not append in list comprehensions but I don't know what to put.

v=[]
p=[]

def listt():
    v=[int(input('Digit element\n'))for j in range(0,int(input('Digit number of elements')))]
    return v
print(listt())

def invert_list(v):
    p=[p.append(v[j]) for j in range(len(v),-1,-1)]
    return p
print(invert_list(v))

Upvotes: 2

Views: 263

Answers (3)

molbdnilo
molbdnilo

Reputation: 66441

p is a local variable; you can't append to it before it exists.

It's not clear why you want the global variables p and v (note that listt does not modify the global v). 

def listt():
     return [int(input('Digit element\n'))for j in range(0,int(input('Digit number of elements')))]

def invert_list(v):
    return [v[j] for j in range(len(v)-1,-1,-1)]

x = listt()
print(x)
print(invert_list(x))

Upvotes: 1

Mehrdad Pedramfar
Mehrdad Pedramfar

Reputation: 11083

Try this instead of p=[p.append(v[j]) for j in range(len(v),-1,-1)]:

p=[v[j] for j in range(len(v),-1,-1)]

Upvotes: 3

Tom Ron
Tom Ron

Reputation: 6181

When you are doing - 

p=[p.append(v[j]) for j in range(len(v),-1,-1)]

p does not exist, hence the error.

You can do the following - 

def invert_list(v):
    p = []
    for j in range(len(v)-1,-1,-1):
         p.append(v[j])
    return p

Upvotes: 1

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