Explanation of error: ‘NoneType’ object is not iterable
In python2, NoneType is the type of None. In Python3 NoneType is the class of None, for example:
>>> print(type(None)) #Python2
<type 'NoneType'> #In Python2 the type of None is the 'NoneType' type.
>>> print(type(None)) #Python3
<class 'NoneType'> #In Python3, the type of None is the 'NoneType' class.
Iterating over a variable that has value None fails:
for a in None:
print("k") #TypeError: 'NoneType' object is not iterable
Python methods return NoneType if they don’t return a value:
def foo():
print("k")
a, b = foo() #TypeError: 'NoneType' object is not iterable
You need to check your looping constructs for NoneType like this:
a = None
print(a is None) #prints True
print(a is not None) #prints False
print(a == None) #prints True
print(a != None) #prints False
print(isinstance(a, object)) #prints True
print(isinstance(a, str)) #prints False
Guido says only use is to check for None because is is more robust to identity checking. Don’t use equality operations because those can spit bubble-up implementationitis of their own. Python’s Coding Style Guidelines — PEP-008
NoneTypes are Sneaky, and can sneak in from lambdas:
import sys
b = lambda x : sys.stdout.write("k")
for a in b(10):
pass #TypeError: 'NoneType' object is not iterable
NoneType is not a valid keyword:
a = NoneType #NameError: name 'NoneType' is not defined
Concatenation of None and a string:
bar = "something"
foo = None
print foo + bar #TypeError: cannot concatenate 'str' and 'NoneType' objects
What’s going on here?
Python’s interpreter converted your code to pyc bytecode. The Python virtual machine processed the bytecode, it encountered a looping construct which said iterate over a variable containing None. The operation was performed by invoking the __iter__ method on the None.
None has no __iter__ method defined, so Python’s virtual machine tells you what it sees: that NoneType has no __iter__ method.
This is why Python’s duck-typing ideology is considered bad. The programmer does something completely reasonable with a variable and at runtime it gets contaminated by None, the python virtual machine attempts to soldier on, and pukes up a bunch of unrelated nonsense all over the carpet.
Java or C++ doesn’t have these problems because such a program wouldn’t be allowed to compile since you haven’t defined what to do when None occurs. Python gives the programmer lots of rope to hang himself by allowing you to do lots of things that should cannot be expected to work under exceptional circumstances. Python is a yes-man, saying yes-sir when it out to be stopping you from harming yourself, like Java and C++ does.
Explanation of error: ‘NoneType’ object is not iterable
In python2, NoneType is the type of None. In Python3 NoneType is the class of None, for example:
>>> print(type(None)) #Python2
<type 'NoneType'> #In Python2 the type of None is the 'NoneType' type.
>>> print(type(None)) #Python3
<class 'NoneType'> #In Python3, the type of None is the 'NoneType' class.
Iterating over a variable that has value None fails:
for a in None:
print("k") #TypeError: 'NoneType' object is not iterable
Python methods return NoneType if they don’t return a value:
def foo():
print("k")
a, b = foo() #TypeError: 'NoneType' object is not iterable
You need to check your looping constructs for NoneType like this:
a = None
print(a is None) #prints True
print(a is not None) #prints False
print(a == None) #prints True
print(a != None) #prints False
print(isinstance(a, object)) #prints True
print(isinstance(a, str)) #prints False
Guido says only use is to check for None because is is more robust to identity checking. Don’t use equality operations because those can spit bubble-up implementationitis of their own. Python’s Coding Style Guidelines — PEP-008
NoneTypes are Sneaky, and can sneak in from lambdas:
import sys
b = lambda x : sys.stdout.write("k")
for a in b(10):
pass #TypeError: 'NoneType' object is not iterable
NoneType is not a valid keyword:
a = NoneType #NameError: name 'NoneType' is not defined
Concatenation of None and a string:
bar = "something"
foo = None
print foo + bar #TypeError: cannot concatenate 'str' and 'NoneType' objects
What’s going on here?
Python’s interpreter converted your code to pyc bytecode. The Python virtual machine processed the bytecode, it encountered a looping construct which said iterate over a variable containing None. The operation was performed by invoking the __iter__ method on the None.
None has no __iter__ method defined, so Python’s virtual machine tells you what it sees: that NoneType has no __iter__ method.
This is why Python’s duck-typing ideology is considered bad. The programmer does something completely reasonable with a variable and at runtime it gets contaminated by None, the python virtual machine attempts to soldier on, and pukes up a bunch of unrelated nonsense all over the carpet.
Java or C++ doesn’t have these problems because such a program wouldn’t be allowed to compile since you haven’t defined what to do when None occurs. Python gives the programmer lots of rope to hang himself by allowing you to do lots of things that should cannot be expected to work under exceptional circumstances. Python is a yes-man, saying yes-sir when it out to be stopping you from harming yourself, like Java and C++ does.
The Python TypeError: NoneType Object Is Not Iterable is an exception that occurs when trying to iterate over a None value. Since in Python, only objects with a value can be iterated over, iterating over a None object raises the TypeError: NoneType Object Is Not Iterable exception.
What Causes TypeError: NoneType Object Is Not Iterable
For an object to be iterable in Python, it must contain a value. Therefore, trying to iterate over a None value raises the Python TypeError: NoneType Object Is Not Iterable exception. Some of the most common sources of None values are:
- Calling a function that does not return anything.
- Calling a function that sets the value of the data to
None. - Setting a variable to
Noneexplicitly.
Python TypeError: NoneType Object Is Not Iterable Example
Here’s an example of a Python TypeError: NoneType Object Is Not Iterable thrown when trying iterate over a None value:
mylist = None
for x in mylist:
print(x)
In the above example, mylist is attempted to be added to be iterated over. Since the value of mylist is None, iterating over it raises a TypeError: NoneType Object Is Not Iterable:
Traceback (most recent call last):
File "test.py", line 3, in <module>
for x in mylist:
TypeError: 'NoneType' object is not iterable
How to Fix TypeError in Python: NoneType Object Is Not Iterable
The Python TypeError: NoneType Object Is Not Iterable error can be avoided by checking if a value is None or not before iterating over it. This can help ensure that only objects that have a value are iterated over, which avoids the error.
Using the above approach, a check can be added to the earlier example:
mylist = None
if mylist is not None:
for x in mylist:
print(x)
Here, a check is performed to ensure that mylist is not None before it is iterated over, which helps avoid the error.
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I am getting a ‘NoneType’ object is not iterable TypeError in the code below. The code below is ment to use pyautogui to scroll through 10 images in the digits folder (named 0 through 9, named with the # in the image) and when ever it finds one, report the value of x along with the number it found. The dictionary is then sorted by x values to read the number found in the image.
Question: I am still learning Python and this TypeError has me stomped, how can I correct this?
#! python3
import sys
import pyautogui
# locate Power
found = dict()
for digit in range(10):
positions = pyautogui.locateOnScreen('digits/{}.png'.format(digit),
region=(888, 920, 150, 40), grayscale=True)
for x, _, _, _ in positions:
found[x] = str(digit)
cols = sorted(found)
value = ''.join(found[col] for col in cols)
print(value)
Traceback of the error:
Traceback (most recent call last):
File "C:\Users\test\python3.6\HC\power.py", line 10, in <module>
for x, _, _, _ in positions:
TypeError: 'NoneType' object is not iterable
The TypeError: 'NoneType' object is not iterable error message is raised when you are trying to iterate over an object that has a value of None, which is not iterable. This means that you are trying to use a for loop or some other kind of iteration on an object that has a value of None, which is not allowed in Python.
Here’s an example of code that will raise this error:
items = None
try:
for item in items:
print(item)
except Exception as e:
print(e)This code will raise the TypeError: 'NoneType' object is not iterable error because the items variable has a value of None, which is not iterable.
To fix this error, you need to make sure that the object you are trying to iterate over is a valid iterable object, such as a list, a tuple, or a string. You can also use an if statement to check if the object is None before attempting to iterate over it.
For example:
items = None
if items is not None:
for item in items:
print(item)
print("done without error")This code will not raise the TypeError error because the if statement will prevent the for loop from being executed if items is None.