Use import module or from module import

Question

I ve tried to find a comprehensive guide on whether it is best to use import module or from module import  I ve just started with Python and I m trying to start off with best practices in mind  Basically  I was hoping if anyone could share their experiences  what preferences other developers have and what s the best way to avoid any gotchas down the road

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As Jan Wrobel mentions  one aspect of the different imports is in which way the imports are disclosed   Module mymath  from math import gcd       Use of mymath   import mymath mymath gcd 30  42     will work though maybe not expected   If I imported gcd only for internal use  not to disclose it to users of mymath  this can be inconvenient  I have this pretty often  and in most cases I want to  keep my modules clean    Apart from the proposal of Jan Wrobel to obscure this a bit more by using import math instead  I have started to hide imports from disclosure by using a leading underscore     for instance    from math import gcd as  gcd   or    import math as  math   In larger projects this  best practice  allows my to exactly control what is disclosed to subsequent imports and what isn t  This keeps my modules clean and pays back at a certain size of project

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import module   Is best when you will use many functions from the module   from module import function   Is best when you want to avoid polluting the global namespace with all the functions and types from a module when you only need function

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The difference between import module and from module import foo is mainly subjective   Pick the one you like best and be consistent in your use of it   Here are some points to help you decide   import module   Pros    Less maintenance of your import statements  Don t need to add any additional imports to start using another item from the module  Cons    Typing module foo in your code can be tedious and redundant  tedium can be minimized by using import module as mo then typing mo foo     from module import foo   Pros    Less typing to use foo More control over which items of a module can be accessed  Cons    To use a new item from the module you have to update your import statement You lose context about foo  For example  it s less clear what ceil   does compared to math ceil      Either method is acceptable  but don t use from module import       For any reasonable large set of code  if you import   you will likely be cementing it into the module  unable to be removed   This is because it is difficult to determine what items used in the code are coming from  module   making it easy to get to the point where you think you don t use the import any more but it s extremely difficult to be sure

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My own answer to this depends mostly on first  how many different modules I ll be using   If i m only going to use one or two  I ll often use from     import since it makes for fewer keystrokes in the rest of the file  but if I m going to make use of many different modules  I prefer just import because that means that each module reference is self-documenting   I can see where each symbol comes from without having to hunt around   Usuaully I prefer the self documenting style of plain import and only change to from   import when the number of times I have to type the module name grows above 10 to 20  even if there s only one module being imported

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import package import module   With import  the token must be a module  a file containing Python commands  or a package  a folder in the sys path containing a file   init   py    When there are subpackages   import package1 package2 package import package1 package2 module   the requirements for folder  package  or file  module  are the same  but the folder or file must be inside package2 which must be inside package1  and both package1 and package2 must contain   init   py files  https   docs python org 2 tutorial modules html  With the from style of import   from package1 package2 import package from package1 package2 import module   the package or module enters the namespace of the file containing the import statement as module  or package  instead of package1 package2 module  You can always bind to a more convenient name   a   big package name subpackage even longer subpackage name function   Only the from style of import permits you to name a particular function or variable   from package3 module import some function   is allowed  but  import package3 module some function    is not allowed

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I personally always use   from package subpackage subsubpackage import module   and then access everything as  module function module modulevar   etc  The reason is that at the same time you have short invocation  and you clearly define the module namespace of each routine  something that is very useful if you have to search for usage of a given module in your source   Needless to say  do not use the import    because it pollutes your namespace and it does not tell you where a given function comes from  from which module   Of course  you can run in trouble if you have the same module name for two different modules in two different packages  like  from package1 subpackage import module from package2 subpackage import module   in this case  of course you run into troubles  but then there s a strong hint that your package layout is flawed  and you have to rethink it

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Both ways are supported for a reason  there are times when one is more appropriate than the other    import module  nice when you are using many bits from the module  drawback is that you ll need to qualify each reference with the module name  from module import      nice that imported items are usable directly without module name prefix  The drawback is that you must list each thing you use  and that it s not clear in code where something came from    Which to use depends on which makes the code clear and readable  and has more than a little to do with personal preference  I lean toward import module generally because in the code it s very clear where an object or function came from  I use from module import     when I m using some object function a lot in the code

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Even though many people already explained about import vs import from  I want to try to explain a bit more about what happens under the hood  and where all the places it changes are   import foo  Imports foo  and creates a reference to that module in the current namespace  Then you need to define completed module path to access a particular attribute or method from inside the module  E g  foo bar but not bar from foo import bar  Imports foo  and creates references to all the members listed  bar   Does not set the variable foo  E g  bar but not baz or foo baz from foo import    Imports foo  and creates references to all public objects defined by that module in the current namespace  everything listed in   all   if   all   exists  otherwise everything that doesn t start with     Does not set the variable foo  E g  bar and baz but not  qux or foo  qux   Now let   s see when we do import X Y   gt  gt  gt  import sys  gt  gt  gt  import os path  Check sys modules with name os and os path   gt  gt  gt  sys modules  os    lt module  os  from   System Library Frameworks Python framework Versions 2 7 lib python2 7 os pyc  gt   gt  gt  gt  sys modules  os path    lt module  posixpath  from   System Library Frameworks Python framework Versions 2 7 lib python2 7 posixpath pyc  gt   Check globals   and locals   namespace dicts with os and os path   gt  gt  gt  globals    os    lt module  os  from   System Library Frameworks Python framework Versions 2 7 lib python2 7 os pyc  gt   gt  gt  gt  locals    os    lt module  os  from   System Library Frameworks Python framework Versions 2 7 lib python2 7 os pyc  gt   gt  gt  gt  globals    os path   Traceback  most recent call last     File  quot  lt stdin gt  quot   line 1  in  lt module gt  KeyError   os path   gt  gt  gt   From the above example we found that only os is inserted in the local and global namespace  So  we should be able to use   gt  gt  gt  os  lt module  os  from     System Library Frameworks Python framework Versions 2 7 lib python2 7 os pyc  gt   gt  gt  gt  os path  lt module  posixpath  from    System Library Frameworks Python framework Versions 2 7 lib python2 7 posixpath pyc  gt   gt  gt  gt   But not path   gt  gt  gt  path Traceback  most recent call last     File  quot  lt stdin gt  quot   line 1  in  lt module gt  NameError  name  path  is not defined  gt  gt  gt   Once you delete the os from locals   namespace  you won t be able to access os as well as os path even though they exist in sys modules   gt  gt  gt  del locals    os    gt  gt  gt  os Traceback  most recent call last     File  quot  lt stdin gt  quot   line 1  in  lt module gt  NameError  name  os  is not defined  gt  gt  gt  os path Traceback  most recent call last     File  quot  lt stdin gt  quot   line 1  in  lt module gt  NameError  name  os  is not defined  gt  gt  gt   Now let s talk about import from  from   gt  gt  gt  import sys  gt  gt  gt  from os import path  Check sys modules with os and os path   gt  gt  gt  sys modules  os    lt module  os  from   System Library Frameworks Python framework Versions 2 7 lib python2 7 os pyc  gt   gt  gt  gt  sys modules  os path    lt module  posixpath  from   System Library Frameworks Python framework Versions 2 7 lib python2 7 posixpath pyc  gt   We found that in sys modules we found as same as we did before by using import name OK  let s check how it looks like in locals   and globals   namespace dicts   gt  gt  gt  globals    path    lt module  posixpath  from   System Library Frameworks Python framework Versions 2 7 lib python2 7 posixpath pyc  gt   gt  gt  gt  locals    path    lt module  posixpath  from   System Library Frameworks Python framework Versions 2 7 lib python2 7 posixpath pyc  gt   gt  gt  gt  globals    os   Traceback  most recent call last     File  quot  lt stdin gt  quot   line 1  in  lt module gt  KeyError   os   gt  gt  gt   You can access by using name path not by os path   gt  gt  gt  path  lt module  posixpath  from   System Library Frameworks Python framework Versions 2 7 lib python2 7 posixpath pyc  gt   gt  gt  gt  os path Traceback  most recent call last     File  quot  lt stdin gt  quot   line 1  in  lt module gt  NameError  name  os  is not defined  gt  gt  gt   Let s delete  path  from locals     gt  gt  gt  del locals    path    gt  gt  gt  path Traceback  most recent call last     File  quot  lt stdin gt  quot   line 1  in  lt module gt  NameError  name  path  is not defined  gt  gt  gt   One final example using an alias   gt  gt  gt  from os import path as HELL BOY  gt  gt  gt  locals    HELL BOY    lt module  posixpath  from   System Library Frameworks Python framework Versions 2 7 lib python2 7 posixpath pyc  gt   gt  gt  gt  globals    HELL BOY    lt module  posixpath  from  System Library Frameworks Python framework Versions 2 7 lib python2 7 posixpath pyc  gt   gt  gt  gt   And no path defined   gt  gt  gt  globals    path   Traceback  most recent call last    File  quot  lt stdin gt  quot   line 1  in  lt module gt  KeyError   path   gt  gt  gt

User · Answer

There are some builtin modules that contain mostly bare functions  base64  math  os  shutil  sys  time       and it is definitely a good practice to have these bare functions bound to some namespace and thus improve the readability of your code  Consider how more difficult is to understand the meaning of these functions without their namespace   copysign foo  bar  monotonic   copystat foo  bar    than when they are bound to some module   math copysign foo  bar  time monotonic   shutil copystat foo  bar    Sometimes you even need the namespace to avoid conflicts between different modules  json load vs  pickle load   On the other hand there are some modules that contain mostly classes  configparser  datetime  tempfile  zipfile       and many of them make their class names self-explanatory enough   configparser RawConfigParser   datetime DateTime   email message EmailMessage   tempfile NamedTemporaryFile   zipfile ZipFile     so there can be a debate whether using these classes with the additional module namespace in your code adds some new information or just lengthens the code

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I ve just discovered one more subtle difference between these two methods   If module foo uses a following import   from itertools import count   Then module bar can by mistake use count as though it was defined in foo  not in itertools   import foo foo count     If foo uses   import itertools   the mistake is still possible  but less likely to be made  bar needs to   import foo foo itertools count     This caused some troubles to me  I had a module that by mistake imported an exception from a module that did not define it  only imported it from other module  using from module import SomeException   When the import was no longer needed and removed  the offending module was broken

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Import Module - You don t need additional efforts to fetch another thing from module  It has disadvantages such as redundant typing   Module Import From - Less typing  amp More control over which items of a module can be accessed To use a new item from the module you have to update your import statement

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Here is another difference not mentioned   This is copied verbatim from http   docs python org 2 tutorial modules html  Note that when using   from package import item   the item can be either a submodule  or subpackage  of the package  or some other name defined in the package  like a function  class or variable  The import statement first tests whether the item is defined in the package  if not  it assumes it is a module and attempts to load it  If it fails to find it  an ImportError exception is raised   Contrarily  when using syntax like   import item subitem subsubitem   each item except for the last must be a package  the last item can be a module or a package but can   t be a class or function or variable defined in the previous item

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One of the significant difference I found out which surprisingly no-one has talked about is that using plain import you can access private variable and private functions from the imported module  which isn t possible with from-import statement      Code in image   setting py  public variable   42  private variable   141 def public function        print  I m a public function  yay    def  private function        print  Ain t nobody accessing me from another module   usually     plain importer py  import settings print  settings  private variable  print  settings public variable  settings public function   settings  private function      Prints    141   42   I m a public function  yay    Ain t nobody accessing me from another module   usually   from importer py  from settings import    print   private variable   doesn t work print  public variable  public function     private function      doesn t work

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I would like to add to this  there are somethings to consider during the import calls   I have the following structure   mod        init   py     main py     a py     b py     c py     d py   main py   import mod a import mod b as b from mod import c import d   dis dis shows the difference     1           0 LOAD CONST               0  -1                3 LOAD CONST               1  None                6 IMPORT NAME              0  mod a                9 STORE NAME               1  mod     2          12 LOAD CONST               0  -1               15 LOAD CONST               1  None               18 IMPORT NAME              2  b               21 STORE NAME               2  b     3          24 LOAD CONST               0  -1               27 LOAD CONST               2    c                  30 IMPORT NAME              1  mod               33 IMPORT FROM              3  c               36 STORE NAME               3  c               39 POP TOP    4          40 LOAD CONST               0  -1               43 LOAD CONST               1  None               46 IMPORT NAME              4  mod d               49 LOAD ATTR                5  d               52 STORE NAME               5  d               55 LOAD CONST               1  None    In the end they look the same  STORE NAME is result in each example   but this is worth noting if you need to consider the following four circular imports   example1  foo       init   py    a py    b py   a py  import foo b    b py  import foo a    gt  gt  gt  import foo a  gt  gt  gt    This works  example2  bar       init   py    a py    b py   a py  import bar b as b   b py  import bar a as a    gt  gt  gt  import bar a Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File  bar a py   line 1  in  lt module gt      import bar b as b   File  bar b py   line 1  in  lt module gt      import bar a as a AttributeError   module  object has no attribute  a    No dice  example3  baz       init   py    a py    b py   a py  from baz import b   b py  from baz import a    gt  gt  gt  import baz a Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File  baz a py   line 1  in  lt module gt      from baz import b   File  baz b py   line 1  in  lt module gt      from baz import a ImportError  cannot import name a   Similar issue    but clearly from x import y is not the same as import import x y as y  example4  qux       init   py    a py    b py   a py  import b    b py  import a    gt  gt  gt  import qux a  gt  gt  gt    This one also works

User · Answer

There s another detail here  not mentioned  related to writing to a module  Granted this may not be very common  but I ve needed it from time to time   Due to the way references and name binding works in Python  if you want to update some symbol in a module  say foo bar  from outside that module  and have other importing code  see  that change  you have to import foo a certain way  For example   module foo   bar    apples    module a   import foo foo bar    oranges      update bar inside foo module object   module b   import foo            print foo bar          if executed after a s  foo bar  assignment  will print  oranges    However  if you import symbol names instead of module names  this will not work   For example  if I do this in module a   from foo import bar bar    oranges    No code outside of a will see bar as  oranges  because my setting of bar merely affected the name  bar  inside module a  it did not  reach into  the foo module object and update its  bar

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Since I am also a beginner  I will be trying to explain this in a simple way  In Python  we have three types of import statements which are  1  Generic imports  import math  this type of import is my personal favorite  the only downside to this import technique is that if you need use any module s function you must use the following syntax  math sqrt 4   of course  it increases the typing effort but as a beginner  it will help you to keep track of module and function associated with it   a good text editor will reduce the typing effort significantly and is recommended   Typing effort can be further reduced by using this import statement  import math as m  now  instead of using math sqrt   you can use m sqrt    2  Function imports  from math import sqrt  this type of import is best suited if your code only needs to access single or few functions from the module  but for using any new item from the module you have to update import statement  3  Universal imports  from math import     Although it reduces typing effort significantly but is not recommended because it will fill your code with various functions from the module and their name could conflict with the name of user-defined functions  example  If you have a function of your very own named sqrt and you import math  your function is safe  there is your sqrt and there is math sqrt  If you do from math import    however  you have a problem  namely  two different functions with the exact same name  Source  Codecademy

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To add to what people have said about from x import    besides making it more difficult to tell where names came from  this throws off code checkers like Pylint   They will report those names as undefined variables

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I was answering a similar question post but the poster deleted it before i could post  Here is one example to illustrate the differences  Python libraries may have one or more files  modules   For exmaples  package1    --   init   py  or package2    --   init   py    -- module1 py    -- module2 py  We can define python functions or classes inside any of the files based design requirements  Let s define  func1   in    init   py under mylibrary1  and foo   in module2 py under mylibrary2   We can access func1   using one of these methods import package1  package1 func1    or import package1 as my  my func1    or from package1 import func1  func1    or from package1 import    func1    We can use one of these methods to access foo    import package2 module2  package2 module2 foo    or import package2 module2 as mod2  mod2 foo    or from package2 import module2  module2 foo    or from package2 import module2 as mod2  mod2 foo    or from package2 module2 import    foo

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since many people answered here but i am just trying my best     import module is best when you don t know which item you have to import from module  In this way it may be difficult to debug when problem raises because you don t know which item have problem   form module import  lt foo gt  is best when you know which item you require to import and also helpful in more controlling using importing specific item according to your need  Using this way debugging may be easy because you know which item you imported

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This is my directory structure of my current directory         -a       -b         -c     The import statement remembers all intermediate names  These names have to be qualified   In 1   import a b c  In 2   a Out 2    lt module  a   namespace  gt   In 3   a b Out 3    lt module  a b   namespace  gt   In 4   a b c Out 4    lt module  a b c   namespace  gt   The from     import     statement remembers only the imported name  This name must not be qualified   In 1   from a b import c  In 2   a NameError  name  a  is not defined  In 2   a b NameError  name  a  is not defined  In 3   a b c NameError  name  a  is not defined  In 4   c Out 4    lt module  a b c   namespace  gt        Note  Of course  I restarted my Python console between steps 1 and 2

[python] Use 'import module' or 'from module import'?

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