Path: csiph.com!newsfeed.hal-mli.net!feeder3.hal-mli.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!news.tele.dk!feed118.news.tele.dk!news.tele.dk!small.news.tele.dk!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.002 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'importing': 0.05; 'found,': 0.07; 'function,': 0.09; 'loaded,': 0.09; 'subject:modules': 0.09; 'cc:addr:python-list': 0.11; 'python': 0.11; 'jan': 0.12; 'cached': 0.16; 'cons': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'module).': 0.16; 'script?': 0.16; 'subject: \n ': 0.16; 'subject:import': 0.16; 'subject:top': 0.16; 'subject:python': 0.16; 'wrote:': 0.18; 'module': 0.19; 'normally': 0.19; 'import': 0.22; 'cc:addr:python.org': 0.22; 'load': 0.23; 'module,': 0.24; 'cc:2**0': 0.24; 'gets': 0.27; 'header:In-Reply-To:1': 0.27; 'function': 0.29; 'especially': 0.30; 'message- id:@mail.gmail.com': 0.30; 'subject:the': 0.34; "can't": 0.35; 'but': 0.35; 'received:google.com': 0.35; 'there': 0.35; 'done': 0.36; 'subject:?': 0.36; 'two': 0.37; 'performance': 0.37; 'pm,': 0.38; 'rather': 0.38; 'that,': 0.38; '12,': 0.39; 'called': 0.40; 'subject:? ': 0.60; 'most': 0.60; 'first': 0.61; 'soon': 0.63; 'sam': 0.68; 'clearer': 0.84; 'to:none': 0.92 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:cc :content-type:content-transfer-encoding; bh=Tgh2HcYD5uSfgk7lmP/tOC2M7hskBriBeG/dnBJMiUo=; b=FtpTBm4RnK1CQ9/+iqmqCQ6Cw5KzZcV4Tr077uXs/iAYYqpqb5KCLpv6WeSw/auGaT cmcAKOCxlPeYOMUpzSOOJQrmW7I+NbzNztuUGDsuo4EE0/rsbZGLIk+KMlPZxZFw1391 Dsvv36rosBZNid9lU+k6F/da8sD6clPJ2bEk5vWVT6LQY1s4F2jyyTQaqOLVQY9iFeiW bQKtJFBiyX1utCH2HqvYMYna9nnZz9J/gY+sVcXkFIQZEkDy11fUnxY5NEL5PPTo1e/R WSJUH2RRtY/EIVzm+6lF1npziRZ8OUMurz+hvZ7P6hZI116eMR543f04IDX2bqIO2YTr Dj8g== MIME-Version: 1.0 X-Received: by 10.66.2.2 with SMTP id 2mr21345840paq.87.1389491290541; Sat, 11 Jan 2014 17:48:10 -0800 (PST) In-Reply-To: References: Date: Sun, 12 Jan 2014 12:48:10 +1100 Subject: Re: Is it better to import python modules inside function or at the top? What are the pros and cons? From: Chris Angelico Cc: "python-list@python.org" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 25 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1389491293 news.xs4all.nl 2965 [2001:888:2000:d::a6]:48108 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:63741 On Sun, Jan 12, 2014 at 12:28 PM, Sam wrote: > I have python modules which are used only in specific functions and the f= unctions are not called all the time. Is it better to import the function i= nside the function only or is it a better practice to always import all mod= ules at the top of the script? If I import the module inside the function, = will it cause a big performance hit because of the import module action tha= t gets to be called every time the function is called? > > What are the pros and cons of each approach? Most of the work of importing is still going to be done only once (after that, the import just grabs a cached reference to the same module). It's normally clearer to import at the top of the module, especially if you have multiple functions calling on the same module, but there are two other concerns: 1) If the module can't be found, would you rather know as soon as your module is loaded, or is it better to load your module without it and then fail only when that function is called? 2) If the module takes a long time to load, would you rather pay that cost as soon as your module is loaded, or on the first use of the function that needs it? ChrisA