Augmented assignment (or compound assignment) is the name given to certain assignment operators in certain programming languages (especially those derived from C). An augmented assignment is generally used to replace a statement where an operator takes a variable as one of its arguments and then assigns the result back to the same variable. A simple example is x += 1 which is expanded to x = x + 1.
Questions tagged [augmented-assignment]
41 questions
171
votes
9 answers
Why does += behave unexpectedly on lists?
The += operator in python seems to be operating unexpectedly on lists. Can anyone tell me what is going on here?
class foo:
bar = []
def __init__(self,x):
self.bar += [x]
class foo2:
bar = []
def __init__(self,x):
…
eucalculia
- 1,727
- 2
- 11
- 6
12
votes
7 answers
Adding a string to a list using augmented assignment
>>> b = []
>>> c = '1234'
>>> b += c
>>> b
['1', '2', '3', '4']
>>>
What is happening here? This should not work, right? Or am I missing something obvious?
>>> b = []
>>> c = '1234'
>>> b + c
Traceback (most recent call last):
File…
joaquin
- 82,968
- 29
- 138
- 152
9
votes
1 answer
Can I use += on multiple variables on one line?
While shortening my code I was cutting down a few variable declarations onto one line-
##For example- going from-
Var1 =15
Var2 = 26
Var3 = 922
##To-
Var1, Var2, Var3 = 15, 26, 922
However, when I tried doing the same thing to this…
Theo Pearson-Bray
- 775
- 1
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- 32
8
votes
1 answer
Is there an equivalent of `sum()` builtin which uses augmented assignment?
Is there any standard library/numpy equivalent of the following function:
def augmented_assignment_sum(iterable, start=0):
for n in iterable:
start += n
return start
?
While sum(ITERABLE) is very elegant, it uses + operator instead…
abukaj
- 2,582
- 1
- 22
- 45
7
votes
2 answers
Python operator precedence with augmented assignment
It seems this question only answered for Java but I would like to know how it works in Python. So are these the same?
a += b / 2
and
a += (b / 2)
Manngo
- 829
- 7
- 24
7
votes
2 answers
python augmented assignment for boolean operators
Does Python have augmented assignment statements corresponding to its boolean operators?
For example I can write this:
x = x + 1
or this:
x += 1
Is there something I can write in place of this:
x = x and y
To avoid writing "x" twice?
Note that…
nonagon
- 3,271
- 1
- 29
- 42
6
votes
3 answers
Why does augmented assignment behave differently when adding a string to a list
I am in a very interesting situation and I am so surprised.
actually I thought both i += 1 and i = i + 1 are same. but it'is not same in here;
a = [1,2]
a += "ali"
and output is [1,2,"a","l","i"]
but if I write like that;
a = [1,2]
a = a +…
Njx
- 121
- 6
4
votes
1 answer
pytorch's augmented assignment and requires_grad
Why does:
with torch.no_grad():
w = w - lr*w.grad
print(w)
results in:
tensor(0.9871)
and
with torch.no_grad():
w -= lr*w.grad
print(w)
results in:
tensor(0.9871, requires_grad=True)
Aren't both operations the same?
Here is…
Tony Power
- 1,033
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- 23
4
votes
1 answer
How can I make a read-only property mutable?
I have two classes, one with an "in-place operator" override (say +=) and another that exposes an instance of the first through a @property. (Note: this is greatly simplified from my actual code to the minimum that reproduces the problem.)
class…
JuSTMOnIcAjUSTmONiCAJusTMoNICa
- 122
- 2
- 10
4
votes
1 answer
Magic method for `self[key] += value`?
There is a Python magic method __setitem__ for assignment = to sequence types. Are there magic methods for augmented assignment += at the container level? The operation does appear to break down gracefully to an augmented assignment of the…
Bob Stein
- 16,271
- 10
- 88
- 101
4
votes
4 answers
How to implement "__iadd__()" for an immutable type?
I would like to subclass an immutable type or implement one of my own which behaves like an int does as shown in the following console session:
>>> i=42
>>> id(i)
10021708
>>> i.__iadd__(1)
Traceback (most recent call last):
File "", line…
martineau
- 119,623
- 25
- 170
- 301
3
votes
6 answers
"+=" causing SyntaxError in Python
n = 1
p = 4
print n += p
gives me:
File "p7.py", line 17
print n += p
SyntaxError: invalid syntax
How can this problem be fixed?
jason
- 4,721
- 8
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- 45
3
votes
1 answer
Python inplace Boolean operator
Python has inplace operators such as -= and |= for arithmetic and bit operations:
FLAG_FOO = 1 << 0
FLAG_BAR = 1 << 1
mask = FLAG_FOO
mask |= FLAG_BAR
assert mask == 3 == FLAG_FOO | FLAG_BAR
Is there an equivalent for actual True/False Booleans?
z0r
- 8,185
- 4
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- 83
3
votes
0 answers
Pycharm unresolved attribute reference warning
Please consider the following code:
import numpy as np
r = [1, 0, -1, 0]
bins = np.fft.fft(r) / len(r)
x = bins.view(float)
Given the above code PyCharm returns this warning: Unresolved attribute reference 'view' for class 'int'
If I split line 4…
MaxPowers
- 5,235
- 2
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- 69
3
votes
4 answers
python list comprehension vs +=
Today I was trying to find a method, to do some processing on strings in python. Some more senior programmer than I'm said not to use += but use ''.join() I could also read this in eg:…
hetepeperfan
- 4,292
- 1
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