Почему важно закрывать файлы?¶
Все открытые файлы автоматически закрываются, когда программа заканчивает работу.
И потому все будет прекрасно работать, пока вы не решите создавать в своей программе промежуточные файлы, информация из которых затем используется в программе.
In [76]:
cat = "cat.txt"
f = open(cat, "w")
f.write("Hello,")
f.write("world\n")
g = open(cat, "r")
print (g.read())
Тут внезапно выяснится, что вы что-то записали в файл, не закрыв его, этого там не оказалось, ваша программа не нашла, чего искала, и упала.
Дело в том, что операции чтения/записи с жесткого диска не являются самыми быстрыми в мире. Потому система предпочитает записывать на жесткий диск не каждый раз, когда вы указали ей это сделать, а ждать, пока не наберется достаточно большой кусок данных. Потому в незакрытый файл вполне возможно запись произведена до конца работы программы и не будет.
А вот если его все же закрыть, то:
In [77]:
f.close()
print (g.read())
g.close()
Hello,world
Более того, часто в биоинформатике вам приходится писать программы, работающие долгое время, возможно, отвечая на тысячи задач. Если так случится, что вы забываете на каждый запрос закрыть файл, то в какой-то момент вы не сможете открыть новый файл и ваша программа завершится аварийно. По-умному такая ситуация называется "утечка файловых дескрипторов".
Демонстрация того, что будет, если открыть слишком много файлов (допустим, на запись, но это верно и для чтения):
In [ ]:
# не запускайте этот код, если не готовы
# перезагружать тетрадь
opened_files = []
for i in range(1, 10000):
fl = open(str(i), "w")
opened_files.append(fl)
Для более наглядного поведения можете запустить скрипт с подобным кодом. Заметьте, что даже открытие одного и того же файла на чтение, но много раз, приводит к проблемам, т.к система позволяет иметь файл открытым множество раз.
In [80]:
open("1.txt", "w").close()
scr = '''
opened_files = []
for i in range(1, 10000):
fl = open('1.txt', "r")
opened_files.append(fl)
''' # another way to define multiline strings in Python
outfile = open("script.py", "w")
outfile.write(scr)
outfile.close()
Запуск команды в jupyter, как в командной строке - для этого просто в начале клетки ставите восклицательный знак
In [81]:
!python script.py
Traceback (most recent call last): File "script.py", line 4, in <module> OSError: [Errno 24] Too many open files: '1.txt'
Исключения¶
В работе с Python мы часто сталкивались с исключительными ситуациями, в которых мы получали ошибки - исключения. Необработанное исключение приходит к завершению Python-программы
In [6]:
a = input()
b = input()
b = int(b)
print(a + b)
5 10
--------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-6-afc0b64be676> in <module>() 2 b = input() 3 b = int(b) ----> 4 print (a + b) TypeError: must be str, not int
Пример хорошей обработки исключений
Медведь убежал из зоопарка, не могут найти.
Наконец звонит бабуля:
— Ой, ко мне во двор медведь забрался и на дерево залез! Уберите его, мне страшно!
Приезжает мужик с маленькой собачкой, даёт бабуле ружье, показывает на собачку и говорит:
— Бабуля, это Кефирчик. Я сейчас залезу наверх, встряхну ветку, медведь свалится, Кефирчик схватит его за ляжку и потащит в зоопарк.
— Хорошо, сынок. А зачем же мне ружье?
— Если вместо медведя свалюсь я, стреляй в Кефирчика!
В Python существует специальный механизм для отлова исключений - try: ... except: ...
In [82]:
1 / 0
--------------------------------------------------------------------------- ZeroDivisionError Traceback (most recent call last) <ipython-input-82-b971f1464605> in <module>() ----> 1 1 / 0 ZeroDivisionError: division by zero
In [58]:
try:
1 / 0
except ZeroDivisionError:
print("HI")
HI
Если не хотим ничего делать
In [ ]:
try:
1 / 0
except ZeroDivisionError:
pass
Порой нам необходимо отловить несколько исключений. В этом случае просто пишем несколько блоков except
In [83]:
a = input()
b = input()
try:
a = int(a) # possible error
b = int(b) # possible error
print (a / b)
except ValueError:
print ("a and b must be integers")
except ZeroDivisionError:
print ("b must be different from 0")
4 9i a and b must be integers
Так же может возникнуть ситуация, когда мы хотим отлавливать исключения, которые являются подтипами друг друга. В этом случае необходимо указывать наиболее частное (ближе к низу в данной диаграмме) исключение первым.
Так не будет работать так, как хотим
In [84]:
a = input()
b = input()
try:
a = int(a) # possible error
b = int(b) # possible error
print (a / b)
print (a[0])
except Exception: # Exception usually is one of the most general Exceptions, it's highly recommended not to use more general exceptions
print ("Other exception")
except ValueError:
print ("a and b must be integers")
except ZeroDivisionError:
print ("b must be different from 0")
p 5 Other exception
А это уже правильная последовательность
In [85]:
a = input()
b = input()
try:
a = int(a) # possible error
b = int(b) # possible error
print (a / b)
print (a[0])
except ValueError:
print ("a and b must be integers")
except ZeroDivisionError:
print ("b must be different from 0")
except Exception: # Exception usually is the most general Exception, it's highly recommended not to use more general exceptions
print ("Other exception")
p 5 a and b must be integers
In [86]:
a = input()
b = input()
try:
a = int(a) # possible error
b = int(b) # possible error
print (a / b)
print (a[0])
except ValueError:
print ("a and b must be integers")
except ZeroDivisionError:
print ("b must be different from 0")
5 8 0.625
--------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-86-07146a9ddd6b> in <module>() 5 b = int(b) # possible error 6 print (a / b) ----> 7 print (a[0]) 8 except ValueError: 9 print ("a and b must be integers") TypeError: 'int' object is not subscriptable
Assert¶
assert позволяет проверить условие и вызвать ошибку, если условие не выполняется:
In [177]:
assert 10==10
In [178]:
assert 10==2
--------------------------------------------------------------------------- AssertionError Traceback (most recent call last) <ipython-input-178-273061a9a3fd> in <module>() ----> 1 assert 10==2 AssertionError:
In [87]:
v1 = 10
v2 = 0
assert v2!=0, 'You passed wrong denominator'
--------------------------------------------------------------------------- AssertionError Traceback (most recent call last) <ipython-input-87-1aed776c1917> in <module>() 1 v1 = 10 2 v2 = 0 ----> 3 assert v2!=0, 'You passed wrong denominator' AssertionError: You passed wrong denominator
Многие используют assert при поиске ошибок в своей программе, что, вообще говоря, неверно, но всех это не очень задевает..
Чтение из сети.¶
Больше информации: https://docs.python.org/3/howto/urllib2.html
In [88]:
import urllib.request
In [89]:
f = urllib.request.urlopen('http://python.org/')
html = f.read()
In [91]:
html
Out[91]:
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title="">User Group Events Archive</a></li>\n \n <li class="tier-2 element-5" role="treeitem"><a href="https://wiki.python.org/moin/PythonEventsCalendar#Submitting_an_Event" title="">Submit an Event</a></li>\n \n</ul>\n\n \n </li>\n \n \n \n \n \n</ul>\n\n \n </nav>\n\n <div class="header-banner "> <!-- for optional "do-not-print" class -->\n \n <div id="dive-into-python" class="flex-slideshow slideshow">\n\n <ul class="launch-shell menu" id="launch-shell">\n <li>\n <a class="button prompt" id="start-shell" data-shell-container="#dive-into-python" href="/shell/">>_\n <span class="message">Launch Interactive Shell</span>\n </a>\n </li>\n </ul>\n\n <ul class="slides menu">\n \n <li>\n <div class="slide-code"><pre><code><span class="comment"># Python 3: Fibonacci series up to n</span>\r\n>>> def fib(n):\r\n>>> a, b = 0, 1\r\n>>> while a < n:\r\n>>> print(a, end=\' \')\r\n>>> a, b = b, a+b\r\n>>> print()\r\n>>> fib(1000)\r\n<span class="output">0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987</span></code></pre></div>\n <div class="slide-copy"><h1>Functions Defined</h1>\r\n<p>The core of extensible programming is defining functions. Python allows mandatory and optional arguments, keyword arguments, and even arbitrary argument lists. <a href="//docs.python.org/3/tutorial/controlflow.html#defining-functions">More about defining functions in Python 3</a></p></div>\n </li>\n \n <li>\n <div class="slide-code"><pre><code><span class="comment"># Python 3: List comprehensions</span>\r\n>>> fruits = [\'Banana\', \'Apple\', \'Lime\']\r\n>>> loud_fruits = [fruit.upper() for fruit in fruits]\r\n>>> print(loud_fruits)\r\n<span class="output">[\'BANANA\', \'APPLE\', \'LIME\']</span>\r\n\r\n<span class="comment"># List and the enumerate function</span>\r\n>>> list(enumerate(fruits))\r\n<span class="output">[(0, \'Banana\'), (1, \'Apple\'), (2, \'Lime\')]</span></code></pre></div>\n <div class="slide-copy"><h1>Compound Data Types</h1>\r\n<p>Lists (known as arrays in other languages) are one of the compound data types that Python understands. Lists can be indexed, sliced and manipulated with other built-in functions. <a href="//docs.python.org/3/tutorial/introduction.html#lists">More about lists in Python 3</a></p></div>\n </li>\n \n <li>\n <div class="slide-code"><pre><code><span class="comment"># Python 3: Simple arithmetic</span>\r\n>>> 1 / 2\r\n<span class="output">0.5</span>\r\n>>> 2 ** 3\r\n<span class="output">8</span>\r\n>>> 17 / 3 <span class="comment"># classic division returns a float</span>\r\n<span class="output">5.666666666666667</span>\r\n>>> 17 // 3 <span class="comment"># floor division</span>\r\n<span class="output">5</span></code></pre></div>\n <div class="slide-copy"><h1>Intuitive Interpretation</h1>\r\n<p>Calculations are simple with Python, and expression syntax is straightforward: the operators <code>+</code>, <code>-</code>, <code>*</code> and <code>/</code> work as expected; parentheses <code>()</code> can be used for grouping. <a href="http://docs.python.org/3/tutorial/introduction.html#using-python-as-a-calculator">More about simple math functions in Python 3</a>.</p></div>\n </li>\n \n <li>\n <div class="slide-code"><pre><code><span class="comment"># Python 3: Simple output (with Unicode)</span>\r\n>>> print("Hello, I\'m Python!")\r\n<span class="output">Hello, I\'m Python!</span>\r\n\r\n<span class="comment"># Input, assignment</span>\r\n>>> name = input(\'What is your name?\\n\')\r\n>>> print(\'Hi, %s.\' % name)\r\n<span class="output">What is your name?\r\nPython\r\nHi, Python.</span></code></pre></div>\n <div class="slide-copy"><h1>Quick & Easy to Learn</h1>\r\n<p>Experienced programmers in any other language can pick up Python very quickly, and beginners find the clean syntax and indentation structure easy to learn. <a href="//docs.python.org/3/tutorial/">Whet your appetite</a> with our Python 3 overview.</p>\r\n </div>\n </li>\n \n <li>\n <div class="slide-code"><pre><code><span class="comment"># For loop on a list</span>\r\n>>> numbers = [2, 4, 6, 8]\r\n>>> product = 1\r\n>>> for number in numbers:\r\n... product = product * number\r\n... \r\n>>> print(\'The product is:\', product)\r\n<span class="output">The product is: 384</span></code></pre></div>\n <div class="slide-copy"><h1>All the Flow You’d Expect</h1>\r\n<p>Python knows the usual control flow statements that other languages speak — <code>if</code>, <code>for</code>, <code>while</code> and <code>range</code> — with some of its own twists, of course. <a href="//docs.python.org/3/tutorial/controlflow.html">More control flow tools in Python 3</a></p></div>\n </li>\n \n </ul>\n </div>\n\n\n </div>\n\n \n <div class="introduction">\n <p>Python is a programming language that lets you work quickly <span class="breaker"></span>and integrate systems more effectively. <a class="readmore" href="/doc/">Learn More</a></p>\n </div>\n\n\n </div><!-- end .container -->\n </header>\n\n <div id="content" class="content-wrapper">\n <!-- Main Content Column -->\n <div class="container">\n\n <section class="main-content " role="main">\n\n \n \n\n \n\n \n\n \n\n <div class="row">\n\n <div class="small-widget get-started-widget">\n <h2 class="widget-title"><span aria-hidden="true" class="icon-get-started"></span>Get Started</h2>\r\n<p>Whether you\'re new to programming or an experienced developer, it\'s easy to learn and use Python.</p>\r\n<p><a href="/about/gettingstarted/">Start with our Beginner’s Guide</a></p>\n </div>\n\n <div class="small-widget download-widget">\n <h2 class="widget-title"><span aria-hidden="true" class="icon-download"></span>Download</h2>\n<p>Python source code and installers are available for download for all versions!</p>\n<p>Latest: <a href="/downloads/release/python-380/">Python 3.8.0</a></p>\n </div>\n\n <div class="small-widget documentation-widget">\n <h2 class="widget-title"><span aria-hidden="true" class="icon-documentation"></span>Docs</h2>\r\n<p>Documentation for Python\'s standard library, along with tutorials and guides, are available online.</p>\r\n<p><a href="https://docs.python.org">docs.python.org</a></p>\n </div>\n\n <div class="small-widget jobs-widget last">\n <h2 class="widget-title"><span aria-hidden="true" class="icon-jobs"></span>Jobs</h2>\r\n<p>Looking for work or have a Python related position that you\'re trying to hire for? Our <strong>relaunched community-run job board</strong> is the place to go.</p>\r\n<p><a href="//jobs.python.org">jobs.python.org</a></p>\n </div>\n\n </div>\n\n <div class="list-widgets row">\n\n <div class="medium-widget blog-widget">\n \n <div class="shrubbery">\n \n <h2 class="widget-title"><span aria-hidden="true" class="icon-news"></span>Latest News</h2>\n <p class="give-me-more"><a href="https://blog.python.org" title="More News">More</a></p>\n \n <ul class="menu">\n \n \n <li>\n<time datetime="2019-10-24T11:30:00.000003+00:00"><span class="say-no-more">2019-</span>10-24</time>\n <a href="http://feedproxy.google.com/~r/PythonSoftwareFoundationNews/~3/OfbgmiSSWnE/chris-angelico-2019-q2-community.html">Chris Angelico: 2019 Q2 Community Service Award Winner</a></li>\n \n <li>\n<time datetime="2019-10-19T22:38:00.000005+00:00"><span class="say-no-more">2019-</span>10-19</time>\n <a href="http://feedproxy.google.com/~r/PythonInsider/~3/NSJOxfu3Kw0/python-2717-released.html">Python 2.7.17 released</a></li>\n \n <li>\n<time datetime="2019-10-16T18:34:59.000002+00:00"><span class="say-no-more">2019-</span>10-16</time>\n <a href="https://mailchi.mp/python/python-software-foundation-q3-newsletter">Python Software Foundation - Q3 Newsletter</a></li>\n \n <li>\n<time datetime="2019-10-15T20:05:00.000001+00:00"><span class="say-no-more">2019-</span>10-15</time>\n <a href="http://feedproxy.google.com/~r/PythonInsider/~3/JAw1EKIElcE/python-375-is-now-available.html">Python 3.7.5 is now available</a></li>\n \n <li>\n<time datetime="2019-10-14T20:45:00+00:00"><span class="say-no-more">2019-</span>10-14</time>\n <a href="http://feedproxy.google.com/~r/PythonInsider/~3/sn3iQBaTaSo/python-380-is-now-available.html">Python 3.8.0 is now available</a></li>\n \n </ul>\n </div><!-- end .shrubbery -->\n\n </div>\n\n <div class="medium-widget event-widget last">\n \n <div class="shrubbery">\n \n <h2 class="widget-title"><span aria-hidden="true" class="icon-calendar"></span>Upcoming Events</h2>\n <p class="give-me-more"><a href="/events/calendars/" title="More Events">More</a></p>\n \n <ul class="menu">\n \n \n \n <li>\n<time datetime="2019-10-31T00:00:00+00:00"><span class="say-no-more">2019-</span>10-31</time>\n <a href="/events/python-events/865/">PyCon Sweden 2019</a></li>\n \n \n \n <li>\n<time datetime="2019-10-31T00:00:00+00:00"><span class="say-no-more">2019-</span>10-31</time>\n <a href="/events/python-events/853/">PyCon Fr</a></li>\n \n \n \n <li>\n<time datetime="2019-11-01T00:00:00+00:00"><span class="say-no-more">2019-</span>11-01</time>\n <a href="/events/python-events/852/">PiterPy 2019</a></li>\n \n \n \n <li>\n<time datetime="2019-11-02T00:00:00+00:00"><span class="say-no-more">2019-</span>11-02</time>\n <a href="/events/python-user-group/863/">Django Girls Groningen</a></li>\n \n \n \n <li>\n<time datetime="2019-11-19T23:00:00+00:00"><span class="say-no-more">2019-</span>11-19</time>\n <a href="/events/python-user-group/870/">Charla Introducci\xc3\xb3n a Python</a></li>\n \n \n </ul>\n </div>\n\n </div>\n\n </div>\n\n <div class="row">\n\n <div class="medium-widget success-stories-widget">\n \n\n\n\n <div class="shrubbery">\n \n\n <h2 class="widget-title"><span aria-hidden="true" class="icon-success-stories"></span>Success Stories</h2>\n <p class="give-me-more"><a href="/success-stories/" title="More Success Stories">More</a></p>\n\n \n <div class="success-story-item" id="success-story-836">\n\n <blockquote>\n <a href="/success-stories/python-seo-link-analyzer/">"Python is all about automating repetitive tasks, leaving more time for your other SEO efforts."</a>\n </blockquote>\n\n <table cellpadding="0" cellspacing="0" border="0" width="100%" class="quote-from">\n <tbody>\n <tr>\n \n <td><p><a href="/success-stories/python-seo-link-analyzer/">Using Python scripts to analyse SEO and broken links on your site</a> <em>by Marnix de Munck</em></p></td>\n </tr>\n </tbody>\n </table>\n </div>\n \n\n </div><!-- end .shrubbery -->\n\n </div>\n\n <div class="medium-widget applications-widget last">\n <div class="shrubbery">\n <h2 class="widget-title"><span aria-hidden="true" class="icon-python"></span>Use Python for…</h2>\r\n<p class="give-me-more"><a href="/about/apps" title="More Applications">More</a></p>\r\n\r\n<ul class="menu">\r\n <li><b>Web Development</b>:\r\n <span class="tag-wrapper"><a class="tag" href="http://www.djangoproject.com/">Django</a>, <a class="tag" href="http://www.pylonsproject.org/">Pyramid</a>, <a class="tag" href="http://bottlepy.org">Bottle</a>, <a class="tag" href="http://tornadoweb.org">Tornado</a>, <a href="http://flask.pocoo.org/" class="tag">Flask</a>, <a class="tag" href="http://www.web2py.com/">web2py</a></span></li>\r\n <li><b>GUI Development</b>:\r\n <span class="tag-wrapper"><a class="tag" href="http://wiki.python.org/moin/TkInter">tkInter</a>, <a class="tag" href="https://wiki.gnome.org/Projects/PyGObject">PyGObject</a>, <a class="tag" href="http://www.riverbankcomputing.co.uk/software/pyqt/intro">PyQt</a>, <a class="tag" href="https://wiki.qt.io/PySide">PySide</a>, <a class="tag" href="https://kivy.org/">Kivy</a>, <a class="tag" href="http://www.wxpython.org/">wxPython</a></span></li>\r\n <li><b>Scientific and Numeric</b>:\r\n <span class="tag-wrapper">\r\n<a class="tag" href="http://www.scipy.org">SciPy</a>, <a class="tag" href="http://pandas.pydata.org/">Pandas</a>, <a href="http://ipython.org" class="tag">IPython</a></span></li>\r\n <li><b>Software Development</b>:\r\n <span class="tag-wrapper"><a class="tag" href="http://buildbot.net/">Buildbot</a>, <a class="tag" href="http://trac.edgewall.org/">Trac</a>, <a class="tag" href="http://roundup.sourceforge.net/">Roundup</a></span></li>\r\n <li><b>System Administration</b>:\r\n <span class="tag-wrapper"><a class="tag" href="http://www.ansible.com">Ansible</a>, <a class="tag" href="http://www.saltstack.com">Salt</a>, <a class="tag" href="https://www.openstack.org">OpenStack</a></span></li>\r\n</ul>\r\n\n </div><!-- end .shrubbery -->\n </div>\n\n </div>\n\n \n <div class="pep-widget">\n\n <h2 class="widget-title">\n <span class="prompt">>>></span> <a href="/dev/peps/">Python Enhancement Proposals<span class="say-no-more"> (PEPs)</span></a>: The future of Python<span class="say-no-more"> is discussed here.</span>\n <a aria-hidden="true" class="rss-link" href="/dev/peps/peps.rss"><span class="icon-feed"></span> RSS</a>\n </h2>\n\n\n \n \n </div>\n\n <div class="psf-widget">\n\n <div class="python-logo"></div>\n \n <h2 class="widget-title">\r\n <span class="prompt">>>></span> <a href="/psf/">Python Software Foundation</a>\r\n</h2>\r\n<p>The mission of the Python Software Foundation is to promote, protect, and advance the Python programming language, and to support and facilitate the growth of a diverse and international community of Python programmers. <a class="readmore" href="/psf/">Learn more</a> </p>\r\n<p class="click-these">\r\n <a class="button" href="/users/membership/">Become a Member</a>\r\n <a class="button" href="/psf/donations/">Donate to the PSF</a>\r\n</p>\n </div>\n\n\n\n\n </section>\n\n \n \n\n \n \n\n\n </div><!-- end .container -->\n </div><!-- end #content .content-wrapper -->\n\n <!-- Footer and social media list -->\n <footer id="site-map" class="main-footer" role="contentinfo">\n <div class="main-footer-links">\n <div class="container">\n\n \n <a id="back-to-top-1" class="jump-link" href="#python-network"><span aria-hidden="true" class="icon-arrow-up"><span>▲</span></span> Back to Top</a>\n\n \n\n<ul class="sitemap navigation menu do-not-print" role="tree" id="container">\n \n <li class="tier-1 element-1">\n <a href="/about/" >About</a>\n \n \n\n<ul class="subnav menu">\n \n <li class="tier-2 element-1" role="treeitem"><a href="/about/apps/" title="">Applications</a></li>\n \n <li class="tier-2 element-2" role="treeitem"><a href="/about/quotes/" 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In [92]:
f = urllib.request.urlopen('http://python.org/')
f.readline()
Out[92]:
b'<!doctype html>\n'
In [93]:
f = urllib.request.urlopen('htp://python.org/')
--------------------------------------------------------------------------- URLError Traceback (most recent call last) <ipython-input-93-c43ca36216fb> in <module>() ----> 1 f = urllib.request.urlopen('htp://python.org/') D:\Devel\Anaconda3\lib\urllib\request.py in urlopen(url, data, timeout, cafile, capath, cadefault, context) 221 else: 222 opener = _opener --> 223 return opener.open(url, data, timeout) 224 225 def install_opener(opener): D:\Devel\Anaconda3\lib\urllib\request.py in open(self, fullurl, data, timeout) 524 req = meth(req) 525 --> 526 response = self._open(req, data) 527 528 # post-process response D:\Devel\Anaconda3\lib\urllib\request.py in _open(self, req, data) 547 548 return self._call_chain(self.handle_open, 'unknown', --> 549 'unknown_open', req) 550 551 def error(self, proto, *args): D:\Devel\Anaconda3\lib\urllib\request.py in _call_chain(self, chain, kind, meth_name, *args) 502 for handler in handlers: 503 func = getattr(handler, meth_name) --> 504 result = func(*args) 505 if result is not None: 506 return result D:\Devel\Anaconda3\lib\urllib\request.py in unknown_open(self, req) 1386 def unknown_open(self, req): 1387 type = req.type -> 1388 raise URLError('unknown url type: %s' % type) 1389 1390 def parse_keqv_list(l): URLError: <urlopen error unknown url type: htp>
In [ ]:
urllib.request.URLError
In [19]:
try:
f = urllib.request.urlopen('htp://python.org/')
except urllib.request.URLError:
print("wrong url")
wrong url
In [94]:
dir(urllib.request)
Out[94]:
['AbstractBasicAuthHandler', 'AbstractDigestAuthHandler', 'AbstractHTTPHandler', 'BaseHandler', 'CacheFTPHandler', 'ContentTooShortError', 'DataHandler', 'FTPHandler', 'FancyURLopener', 'FileHandler', 'HTTPBasicAuthHandler', 'HTTPCookieProcessor', 'HTTPDefaultErrorHandler', 'HTTPDigestAuthHandler', 'HTTPError', 'HTTPErrorProcessor', 'HTTPHandler', 'HTTPPasswordMgr', 'HTTPPasswordMgrWithDefaultRealm', 'HTTPPasswordMgrWithPriorAuth', 'HTTPRedirectHandler', 'HTTPSHandler', 'MAXFTPCACHE', 'OpenerDirector', 'ProxyBasicAuthHandler', 'ProxyDigestAuthHandler', 'ProxyHandler', 'Request', 'URLError', 'URLopener', 'UnknownHandler', '__all__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', '__version__', '_cut_port_re', '_ftperrors', '_have_ssl', '_localhost', '_noheaders', '_opener', '_parse_proxy', '_proxy_bypass_macosx_sysconf', '_randombytes', '_safe_gethostbyname', '_thishost', '_url_tempfiles', 'addclosehook', 'addinfourl', 'base64', 'bisect', 'build_opener', 'collections', 'contextlib', 'email', 'ftpcache', 'ftperrors', 'ftpwrapper', 'getproxies', 'getproxies_environment', 'getproxies_registry', 'hashlib', 'http', 'install_opener', 'io', 'localhost', 'noheaders', 'os', 'parse_http_list', 'parse_keqv_list', 'pathname2url', 'posixpath', 'proxy_bypass', 'proxy_bypass_environment', 'proxy_bypass_registry', 'quote', 're', 'request_host', 'socket', 'splitattr', 'splithost', 'splitpasswd', 'splitport', 'splitquery', 'splittag', 'splittype', 'splituser', 'splitvalue', 'ssl', 'string', 'sys', 'tempfile', 'thishost', 'time', 'to_bytes', 'unquote', 'unquote_to_bytes', 'unwrap', 'url2pathname', 'urlcleanup', 'urljoin', 'urlopen', 'urlparse', 'urlretrieve', 'urlsplit', 'urlunparse', 'warnings']
In [1]:
import math
In [3]:
math.log(28)
Out[3]:
3.332204510175204
In [4]:
math.sqrt(2)
Out[4]:
1.4142135623730951
In [7]:
math.log(10, 10)
--------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-7-11de8836f9ba> in <module>() ----> 1 math.log(10, 10) TypeError: 'int' object is not callable
In [6]:
math.log = 10
In [ ]:
math.log10(10)
In [8]:
import random
In [9]:
random
Out[9]:
<module 'random' from 'D:\\Devel\\Anaconda3\\lib\\random.py'>
In [15]:
random.choice([1, 2, 3, -10])
Out[15]:
2
In [ ]:
random.
In [17]:
from random import choice
from random import random
In [18]:
random()
Out[18]:
0.3848387110519822
In [19]:
?random
In [21]:
a = []
p = 0.5
In [22]:
for i in range(20):
if random() < p:
a.append(0)
else:
a.append(1)
In [23]:
a
Out[23]:
[1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1]
In [58]:
from random import choice, random, sample
In [65]:
In [24]:
a = []
alphabet = "ATGC"
for i in range(20):
al = choice(alphabet)
a.append(al)
In [25]:
a
Out[25]:
['A', 'C', 'A', 'A', 'T', 'A', 'A', 'A', 'T', 'A', 'G', 'C', 'T', 'G', 'T', 'G', 'C', 'G', 'C', 'C']
In [72]:
"".join(a)
Out[72]:
'CACCTGCGGTCGTACTACTG'
In [27]:
"yeah".join(a)
Out[27]:
'AyeahCyeahAyeahAyeahTyeahAyeahAyeahAyeahTyeahAyeahGyeahCyeahTyeahGyeahTyeahGyeahCyeahGyeahCyeahC'
sys.argv¶
In [28]:
from sys import argv
In [29]:
argv
Out[29]:
['D:\\Devel\\Anaconda3\\lib\\site-packages\\ipykernel_launcher.py', '-f', 'C:\\Users\\pdd\\AppData\\Roaming\\jupyter\\runtime\\kernel-7cdc5d93-ae37-491c-9dfd-dea7fadbb740.json']
In [30]:
scr = '''
from sys import argv
print(argv)
''' # another way to define multiline strings in Python
outfile = open("script_argv1.py", "w")
outfile.write(scr)
outfile.close()
In [31]:
!python script_argv1.py hello,\ Dima trash spec
['script_argv1.py', 'hello,\\', 'Dima', 'trash', 'spec']
In [32]:
scr = '''
from sys import argv
try:
i = int(argv[1])
j = int(argv[2])
print(i, "*", j, "=", i * j)
except:
print("Non-integers")
''' # another way to define multiline strings in Python
outfile = open("script_argv2.py", "w")
outfile.write(scr)
outfile.close()
In [33]:
!python script_argv2.py 10 8 hello,\ Dima
10 * 8 = 80
In [34]:
!python script_argv2.py a 60 hello,\ Dima
Non-integers
In [ ]: