Strange logic! :)

[alsimm]

Hi all
python 2.7
can someone explain the logic here I am confused (doesn't take much to confuse me
In the first example everything works OK.But the second example despite the fact that x is a variable
it doesn't work.Now the question here is this...does python have strange logic...or do I
example 1

a = 1
print a
a +=1
print a

example 2

e = 10
print e
x = e +=1
print x

kind regards
al

[buran]

In example 2, line 3

x = e +=1

rise SyntaxError: Invalid syntax (of course).


What you expect this line to do?

[idontreallywolf]

You are allowed to do:

x = e+1

but not

x = e += 1

because x = e += 1 is same as
x = e = e + 1

[buran]

because x = e += 1 is same as
x = e = e + 1

actually, the first one is invalid syntax and rise SynatxError,
while second one is perfectly fine

e = 10
x = e = e + 1
print x
print e

Output:
11
11

[idontreallywolf]

because x = e += 1 is same as
x = e = e + 1

actually, the first one is invalid syntax and rise SynatxError,
while second one is perfectly fine

e = 10
x = e = e + 1
print x
print e

Output:
11
11

Then why would x = e += 1 be invalid if its the same as x = e = e + 1 ?

[buran]

Then why would x = e += 1 be invalid if its the same as x = e = e + 1 ?

You are the one that repeatedly claims they are the same, not me.... :-)

x = e = e + 1 is called chained assignment and is valid python code.

[volcano63]

Then why would x = e += 1 be invalid if its the same as x = e = e + 1 ?

You are the one that repeatedly claims they are the same, not me.... :-)

x = e = e + 1 is called chained assignment and is valid python code.

Assignment in Python - unlike in C - does not return value - that why in Python if x=3 is illegal too, and Python programmers don't have to write

if 3 == x

in

x = e += 1

right operand is assignment - unlike in the example above, where right operand is e + 1

[buran]

@volcano63, I don't understand what you mean that Python programmers don't have to write if 3 == x and once again x = e += 1 is invalid, raising SyntaxError.

[volcano63]

@volcano63, I don't understand what you mean that Python programmers don't have to write if 3 == x

Many C/C++ programmers acquire the habit to write if (3 == x) instead of if (x == 3), because if you accidentally omit =, the code will still compile - but the meaning will change.

if (3 = x) is illegal assignment, failing compilation.

and once again x = e += 1 is invalid, raising SyntaxError.

I thought I was enhancing your point, not arguing it.

[nilamo]

if (3 = x) is illegal assignment, failing compilation.

I do this all the time, because I like when the compiler tells me I'm stupid. I believe it's commonly referred to as yoda checking, because it sounds backwards. (https://en.wikipedia.org/wiki/Yoda_conditions)