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I don't understand the following from pep-0404

In Python 3, implicit relative imports within packages are no longer available - only absolute imports and explicit relative imports are supported. In addition, star imports (e.g. from x import *) are only permitted in module level code.

What is a relative import? In what other places star import was allowed in python2? Please explain with examples.

Relative import happens whenever you are importing a package relative to the current script/package.

Consider the following tree for example:

mypkg
├── base.py
└── derived.py

Now, your derived.py requires something from base.py. In Python 2, you could do it like this (in derived.py):

from base import BaseThing

Python 3 no longer supports that since it's not explicit whether you want the 'relative' or 'absolute' base. In other words, if there was a Python package named base installed in the system, you'd get the wrong one.

Instead it requires you to use explicit imports which explicitly specify location of a module on a path-alike basis. Your derived.py would look like:

from .base import BaseThing

The leading . says 'import base from module directory'; in other words, .base maps to ./base.py.

Similarly, there is .. prefix which goes up the directory hierarchy like ../ (with ..mod mapping to ../mod.py), and then ... which goes two levels up (../../mod.py) and so on.

Please however note that the relative paths listed above were relative to directory where current module (derived.py) resides in, not the current working directory.


@BrenBarn has already explained the star import case. For completeness, I will have to say the same ;).

For example, you need to use a few math functions but you use them only in a single function. In Python 2 you were permitted to be semi-lazy:

def sin_degrees(x):
    from math import *
    return sin(degrees(x))

Note that it already triggers a warning in Python 2:

a.py:1: SyntaxWarning: import * only allowed at module level
  def sin_degrees(x):

In modern Python 2 code you should and in Python 3 you have to do either:

def sin_degrees(x):
    from math import sin, degrees
    return sin(degrees(x))

or:

from math import *

def sin_degrees(x):
    return sin(degrees(x))

5. The import system, Python 3 brings a complete overhaul of the way import works – the import machinery was ported from C to Developer-visible changes are summarised below. Given the structure above, these statements would be equivalent (in core.py ):. The import statement combines two operations; it searches for the named module, then it binds the results of that search to a name in the local scope. The search operation of the import statement is defined as a call to the __import__ () function, with the appropriate arguments.

For relative imports see the documentation. A relative import is when you import from a module relative to that module's location, instead of absolutely from sys.path.

As for import *, Python 2 allowed star imports within functions, for instance:

>>> def f():
...     from math import *
...     print sqrt

A warning is issued for this in Python 2 (at least recent versions). In Python 3 it is no longer allowed and you can only do star imports at the top level of a module (not inside functions or classes).

Importing, file, this will be declared at the top of the code, under any shebang lines or general comments. The import statement allows you to import one or more modules into your Python program, letting you make use of the definitions constructed in those modules. Using from … import. To refer to items from a module within your program’s namespace, you can use the from … import statement. When you import modules this way, you can refer to the functions by name rather than through dot notation

To support both Python 2 and Python 3, use explicit relative imports as below. They are relative to the current module. They have been supported starting from 2.5.

from .sister import foo
from . import brother
from ..aunt import bar
from .. import uncle

Absolute vs Relative Imports in Python – Real Python, statement is defined as a call to the __import__() function, with the appropriate arguments. In Python 2, one could write from <module> import * within a function. In Python 3, the from <module> import * syntax is only allowed at the module level, no longer inside functions. Sources: Changes in import statement python3; Python 2 modules documentation; Python 3 modules documentation; What’s New in Python 3.0; Appendix: List of Always Built-in Modules

Added another case to Michał Górny's answer:

Note that relative imports are based on the name of the current module. Since the name of the main module is always "__main__", modules intended for use as the main module of a Python application must always use absolute imports.

The Definitive Guide to Python import Statements, is a convenience to the programmer and is not technically needed to write complete Java program. To check if an object is a file, as in isinstance(f, file). The recommended fixer addresses the first use: it will rewrite all calls to file() to open() . If your code uses the name file for a different function, you will need to revert the fixer’s change. The fixer does not address the second case.

How To Import Modules in Python 3, any packages that have been installed to those locations. Changes Already Present In Python 2.6¶ Since many users presumably make the jump straight from Python 2.5 to Python 3.0, this section reminds the reader of new features that were originally designed for Python 3.0 but that were back-ported to Python 2.6.

Java import Statement, This has changed in Python 3.3: now any directory on sys.path with a name that matches python3 -c "import example.foo" Hello from example.foo complaining about relative imports in a non-package or beyond the top-level package for  The import statement has two problems: Long import statements can be difficult to write, requiring various contortions to fit Pythonic style guidelines. Imports can be ambiguous in the face of packages; within a package, it's not clear whether import foo refers to a module within the package or some module outside the package.

How does python find packages? // Lee On Coding // My blog about , py files or via the Python command line interpreter. In Python, modules are accessed by using the import statement. When you do this, you  Additionally, absolute imports remain valid even if the current location of the import statement changes. In fact, PEP 8 explicitly recommends absolute imports. Sometimes, however, absolute imports can get quite verbose, depending on the complexity of the directory structure.

Comments
  • Why was that decision made?
  • My guess is that idea behind it is 'Explicit is better than implicit.' from PEP20 - The Zen of Python. Dot before module makes relative/nonrelative linking explicit thus resolving possible name collisions. Although 'Readability counts.' suffers slightly.
  • No, in fact it was the "opposite", "practicality beats purity" decision. That was necessary in order to optimize local variable access inside functions, since without "import *", compiler always knows just by analyzing the code, what variables are local and can be looked up directly. In fact, functions don't even use a dict for local storage, but an optimized array where variables get unique indices.
  • import .brother gives me an invalid syntax error in Python 3.5. This is normal? I have init.py in the directory it is in
  • import .brother is invalid syntax for both python 2 and 3
  • @RodrigoE.Principe and so seems to be import ..uncle. Fixed. Oh, what have I been thinking... probably got distracted by the knights who say Ni!