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Constructing variables within a for loop

0

Let's say I want to create a lot of instances of a class but don't want to write the variable name down for every instance.

What I want:

value1 = class(value1)
value2 = class(value2)
.
.
. 

My idea was:

list = ['One','Two','Three']

for value in list:
 value = class(value)

The result is not what I wanted. Python creates the variable 'value' and overrides it with the values of the list.

I'm sorry to ask such a basic question, but I'm not sure how to handle this.

python oop for-loop instance

share|improve this question

edited Mar 21 at 18:24

petezurich

3,76581936

asked Mar 21 at 18:08

Blue SkyBlue Sky

31

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Use a container like a list or a dict, in this case, a list seems appropriate
  
  – juanpa.arrivillaga
  Mar 21 at 18:09
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  values = [class(x) for x in list]
  
  – Blorgbeard
  Mar 21 at 18:13
  

  
  
  
  

add a comment | 

0

Let's say I want to create a lot of instances of a class but don't want to write the variable name down for every instance.

What I want:

value1 = class(value1)
value2 = class(value2)
.
.
. 

My idea was:

list = ['One','Two','Three']

for value in list:
 value = class(value)

The result is not what I wanted. Python creates the variable 'value' and overrides it with the values of the list.

I'm sorry to ask such a basic question, but I'm not sure how to handle this.

python oop for-loop instance

share|improve this question

edited Mar 21 at 18:24

petezurich

3,76581936

asked Mar 21 at 18:08

Blue SkyBlue Sky

31

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Use a container like a list or a dict, in this case, a list seems appropriate
  
  – juanpa.arrivillaga
  Mar 21 at 18:09
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  values = [class(x) for x in list]
  
  – Blorgbeard
  Mar 21 at 18:13
  

  
  
  
  

add a comment | 

Let's say I want to create a lot of instances of a class but don't want to write the variable name down for every instance.

What I want:

value1 = class(value1)
value2 = class(value2)
.
.
. 

My idea was:

list = ['One','Two','Three']

for value in list:
 value = class(value)

The result is not what I wanted. Python creates the variable 'value' and overrides it with the values of the list.

I'm sorry to ask such a basic question, but I'm not sure how to handle this.

python oop for-loop instance

share|improve this question

edited Mar 21 at 18:24

petezurich

3,76581936

asked Mar 21 at 18:08

Blue SkyBlue Sky

31

value1 = class(value1)
value2 = class(value2)
.
.
. 

list = ['One','Two','Three']

for value in list:
 value = class(value)

share|improve this question

edited Mar 21 at 18:24

petezurich

3,76581936

asked Mar 21 at 18:08

Blue SkyBlue Sky

31

share|improve this question

edited Mar 21 at 18:24

petezurich

3,76581936

asked Mar 21 at 18:08

Blue SkyBlue Sky

31

edited Mar 21 at 18:24

petezurich

3,76581936

edited Mar 21 at 18:24

petezurich

3,76581936

asked Mar 21 at 18:08

Blue SkyBlue Sky

31

asked Mar 21 at 18:08

Blue SkyBlue Sky

31

2 Answers
2

active

oldest

votes

1

First of all, note that you should not use list as a variable name, as it is reserved as a keyword by Python itself. Then, you could have another list, instanceList lets say, in which you will append every newly created instance of a class:

myList = ['One','Two','Three']
instanceList = []

for value in myList:
 instanceList.append(class(value))

share|improve this answer

answered Mar 21 at 18:17

Vasilis G.Vasilis G.

3,9942924

add a comment | 

1

You can use a list comprehension to build a list of class instances from a list of values:

class A:
 def __init__(self, value):
 self.value = value

values = ['One','Two','Three']
instances = [A(v) for v in values]

>>> print(list(o.value for o in instances))
['One', 'Two', 'Three']

share|improve this answer

answered Mar 21 at 18:17

cglacetcglacet

1,240819

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That is a generator expression, not a list comprehension...
  
  – juanpa.arrivillaga
  Mar 21 at 18:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  [A(v) for v in values] is a list comprehension - he just uses a generator expression to print the results.
  
  – Blorgbeard
  Mar 21 at 18:19
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I'm not sure to understand your question/remark, but if you need a generator instead of a list, then you can just replace instances = [...] by instances = (...). Another legitimate option is to use a for-loop as mentioned in this answer.
  
  – cglacet
  Mar 21 at 18:21
  
  

  
  
  
  

add a comment | 

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1

First of all, note that you should not use list as a variable name, as it is reserved as a keyword by Python itself. Then, you could have another list, instanceList lets say, in which you will append every newly created instance of a class:

myList = ['One','Two','Three']
instanceList = []

for value in myList:
 instanceList.append(class(value))

share|improve this answer

answered Mar 21 at 18:17

Vasilis G.Vasilis G.

3,9942924

add a comment | 

1

First of all, note that you should not use list as a variable name, as it is reserved as a keyword by Python itself. Then, you could have another list, instanceList lets say, in which you will append every newly created instance of a class:

myList = ['One','Two','Three']
instanceList = []

for value in myList:
 instanceList.append(class(value))

share|improve this answer

answered Mar 21 at 18:17

Vasilis G.Vasilis G.

3,9942924

add a comment | 

First of all, note that you should not use list as a variable name, as it is reserved as a keyword by Python itself. Then, you could have another list, instanceList lets say, in which you will append every newly created instance of a class:

myList = ['One','Two','Three']
instanceList = []

for value in myList:
 instanceList.append(class(value))

share|improve this answer

answered Mar 21 at 18:17

Vasilis G.Vasilis G.

3,9942924

myList = ['One','Two','Three']
instanceList = []

for value in myList:
 instanceList.append(class(value))

share|improve this answer

answered Mar 21 at 18:17

Vasilis G.Vasilis G.

3,9942924

answered Mar 21 at 18:17

Vasilis G.Vasilis G.

3,9942924

answered Mar 21 at 18:17

Vasilis G.Vasilis G.

3,9942924

1

You can use a list comprehension to build a list of class instances from a list of values:

class A:
 def __init__(self, value):
 self.value = value

values = ['One','Two','Three']
instances = [A(v) for v in values]

>>> print(list(o.value for o in instances))
['One', 'Two', 'Three']

share|improve this answer

answered Mar 21 at 18:17

cglacetcglacet

1,240819

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That is a generator expression, not a list comprehension...
  
  – juanpa.arrivillaga
  Mar 21 at 18:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  [A(v) for v in values] is a list comprehension - he just uses a generator expression to print the results.
  
  – Blorgbeard
  Mar 21 at 18:19
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I'm not sure to understand your question/remark, but if you need a generator instead of a list, then you can just replace instances = [...] by instances = (...). Another legitimate option is to use a for-loop as mentioned in this answer.
  
  – cglacet
  Mar 21 at 18:21
  
  

  
  
  
  

add a comment | 

1

You can use a list comprehension to build a list of class instances from a list of values:

class A:
 def __init__(self, value):
 self.value = value

values = ['One','Two','Three']
instances = [A(v) for v in values]

>>> print(list(o.value for o in instances))
['One', 'Two', 'Three']

share|improve this answer

answered Mar 21 at 18:17

cglacetcglacet

1,240819

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That is a generator expression, not a list comprehension...
  
  – juanpa.arrivillaga
  Mar 21 at 18:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  [A(v) for v in values] is a list comprehension - he just uses a generator expression to print the results.
  
  – Blorgbeard
  Mar 21 at 18:19
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I'm not sure to understand your question/remark, but if you need a generator instead of a list, then you can just replace instances = [...] by instances = (...). Another legitimate option is to use a for-loop as mentioned in this answer.
  
  – cglacet
  Mar 21 at 18:21
  
  

  
  
  
  

add a comment | 

You can use a list comprehension to build a list of class instances from a list of values:

class A:
 def __init__(self, value):
 self.value = value

values = ['One','Two','Three']
instances = [A(v) for v in values]

>>> print(list(o.value for o in instances))
['One', 'Two', 'Three']

share|improve this answer

answered Mar 21 at 18:17

cglacetcglacet

1,240819

class A:
 def __init__(self, value):
 self.value = value

values = ['One','Two','Three']
instances = [A(v) for v in values]

>>> print(list(o.value for o in instances))
['One', 'Two', 'Three']

share|improve this answer

answered Mar 21 at 18:17

cglacetcglacet

1,240819

answered Mar 21 at 18:17

cglacetcglacet

1,240819

answered Mar 21 at 18:17

cglacetcglacet

1,240819