python-internals

I noticed that without source code encoding declaration, the Python 2 interpreter assumes the source code is encoded in ASCII with scripts and standard input : $ python test.py # where test.py holds the line: print u'é' File "test.py", line 1 SyntaxError: Non-ASCII character '\xc3' in file test.py on line 1, but no encoding declared; see http://python.org/dev/peps/pep-0263/ for details $ echo "print u'é'" | python File "/dev/fd/63", line 1 SyntaxError: Non-ASCII character '\xc3' in file /dev/fd/63 on line 1, but no encoding declared; see http://python.org/dev/peps/pep-0263/ for details and it

I would like to see how str.split() is implemented in Python Here's what I tried: > inspect.getsource(str.split) TypeError: <method 'split' of 'str' objects> is not a module, class, method, function, traceback, frame, or code object Copying the other example on StackOverflow has not work: Code for Greatest Common Divisor in Python inspect.getsource(str.split) is not written to handle code written in the implementation language ( C here). str.split is builtin , i.e written in C . The source code for the implementation of str.split is broken up in two parts based on if a sep argument is supplied

I'm looking into these two related questions: here and here . I am seeing a behavior I do not expect in Python 3.6, which differs from behavior using plain reload in Python 2.7 (and 3.4). Namely, it seems that a module attribute that would be populated during module initialization or when re-exec-ing the module during a reload, is not restored after its local name is removed with del ... see below: For Python 3.6: In [1]: import importlib In [2]: import math In [3]: del math.cos In [4]: math.cos --------------------------------------------------------------------------- AttributeError

This question already has an answer here: How does exec work with locals? 3 answers Why does the following python3 code produces an error? a=''' def x(): print(42) ''' class Test: def __init__(self): exec(a) x() t = Test() Results in this message: Traceback (most recent call last): File "bug.py", line 11, in <module> t = Test() File "bug.py", line 9, in __init__ x() NameError: global name 'x' is not defined Note: exec was just a Simple statement in Python 2.x, whereas it is a function in Python 3.x. Python 2.7 Let us check the changes made by executing a . class Test: def __init__(self): l, g

So lists are unhashable: >>> { [1,2]:3 } TypeError: unhashable type: 'list' The following page gives an explanation: A list is a mutable type, and cannot be used as a key in a dictionary (it could change in-place making the key no longer locatable in the internal hash table of the dictionary). I understand why it is undesirable to use mutable objects as dictionary keys. However, Python raises the same exception even when I am simply trying to hash a list (independently of dictionary creation) >>> hash( [1,2] ) TypeError: unhashable type: 'list' Does Python do this as a guarantee that mutable

I'm iterating a list as follows: some_list = [1, 2, 3, 4] another_list = [1, 2, 3, 4] for idx, item in enumerate(some_list): del some_list[idx] for item in another_list: another_list.remove(item) When I print out the contents of the lists >>> some_list [2, 4] >>> another_list [2, 4] I'm aware that Python doesn't support modifying a list while iterating over it and the right way is to iterate over copy of list instead (so please don't downvote). But I want to know what exactly happens behind the scenes i.e. Why is the output of the above snippet [2, 4] ? You can use a self-made iterator that