{"id":4875,"date":"2021-09-20T08:00:37","date_gmt":"2021-09-20T08:00:37","guid":{"rendered":"https:\/\/tst-amo.net.ua\/blog\/?p=4875"},"modified":"2021-09-24T10:55:35","modified_gmt":"2021-09-24T10:55:35","slug":"4875","status":"publish","type":"post","link":"https:\/\/tst-amo.net.ua\/blog\/?p=4875","title":{"rendered":"Python3"},"content":{"rendered":"

\u0412\u0441\u0442\u0440\u043e\u0435\u043d\u043d\u044b\u0435 \u043e\u0431\u044a\u0435\u043a\u0442\u044b<\/h3>\n
Object type        Example literals\/creation\r\nNumbers            1234, 3.1415, 3+4j, 0b111, Decimal(), Fraction()\r\nStrings            'spam', \"Bob's\", b'a\\x01c', u'sp\\xc4m'\r\nLists              [1, [2, 'three'], 4.5], list(range(10))\r\nDictionaries       {'food': 'spam', 'taste': 'yum'}, dict(hours=10)\r\nTuples             (1, 'spam', 4, 'U'), tuple('spam'), namedtuple\r\nFiles              open('eggs.txt'), open(r'C:\\ham.bin', 'wb')\r\nSets               set('abc'), {'a', 'b', 'c'}\r\nOther core types   Booleans, types, None<\/pre>\n
Numbers<\/h4>\n
>>> 123 + 222 # Integer addition\r\n345\r\n>>> 1.5 * 4 # Floating-point multiplication\r\n6.0\r\n>>> 2 ** 100 # 2 to the power 100, again\r\n1267650600228229401496703205376<\/pre>\n
>>> len(str(2 ** 1000000)) # How many digits in a really BIG number?\r\n301030<\/pre>\n
start experimenting with floating-point\r\nnumbers, you\u2019re likely to stumble across something that may look a bit odd at first\r\nglance:\r\n>>> 3.1415 * 2 # repr: as code (Pythons < 2.7 and 3.1)\r\n6.2830000000000004\r\n>>> print(3.1415 * 2) # str: user-friendly\r\n6.283<\/pre>\n
>>> import math\r\n>>> math.pi\r\n3.141592653589793\r\n>>> math.sqrt(85)\r\n9.219544457292887<\/pre>\n
>>> import random\r\n>>> random.random()\r\n0.7082048489415967\r\n>>> random.choice([1, 2, 3, 4])\r\n1<\/pre>\n
String<\/h4>\n
>>> S = 'Spam' # Make a 4-character string, and assign it to a name\r\n>>> len(S) # Length\r\n4\r\n>>> S[0] # The first item in S, indexing by zero-based position\r\n'S'\r\n>>> S[1] # The second item from the left\r\n'p'<\/pre>\n
In Python, we can also index backward, from the end\u2014positive indexes count from
\nthe left, and negative indexes count back from the right:<\/p>\n
>>> S[-1] # The last item from the end in S\r\n'm'\r\n>>> S[-2] # The second-to-last item from the end\r\n'a'<\/pre>\n
Formally, a negative index is simply added to the string\u2019s length, so the following two
\noperations are equivalent (though the first is easier to code and less easy to get wrong):<\/p>\n
>>> S[-1] # The last item in S\r\n'm'\r\n>>> S[len(S)-1] # Negative indexing, the hard way\r\n'm'<\/pre>\n
In addition to simple positional indexing, sequences also support a more general form
\nof indexing known as slicing, which is a way to extract an entire section (slice) in a single
\nstep. For example:<\/p>\n
>>> S # A 4-character string\r\n'Spam'\r\n>>> S[1:3] # Slice of S from offsets 1 through 2 (not 3)\r\n'pa'<\/pre>\n
>>> S[1:] # Everything past the first (1:len(S))\r\n'pam'\r\n>>> S # S itself hasn't changed\r\n'Spam'\r\n>>> S[0:3] # Everything but the last\r\n'Spa'\r\n>>> S[:3] # Same as S[0:3]\r\n'Spa'\r\n>>> S[:-1] # Everything but the last again, but simpler (0:-1)\r\n'Spa'\r\n>>> S[:] # All of S as a top-level copy (0:len(S))\r\n'Spam'<\/pre>\n
>>> S + 'xyz' # Concatenation\r\n'Spamxyz'\r\n>>> S # S is unchanged\r\n'Spam'\r\n>>> S * 8 # Repetition\r\n'SpamSpamSpamSpamSpamSpamSpamSpam'<\/pre>\n
Immutability<\/h4>\n
Also notice in the prior examples that we were not changing the original string with
\nany of the operations we ran on it. Every string operation is defined to produce a new
\nstring as its result, because strings are immutable in Python\u2014they cannot be changed
\nin place after they are created. In other words, you can never overwrite the values of
\nimmutable objects. For example, you can\u2019t change a string by assigning to one of its
\npositions, but you can always build a new one and assign it to the same name. Because
\nPython cleans up old objects as you go (as you\u2019ll see later), this isn\u2019t as inefficient as it
\nmay sound:<\/p>\n
>>> S\r\n'Spam'\r\n>>> S[0] = 'z' # Immutable objects cannot be changed\r\n...error text omitted...\r\nTypeError: 'str' object does not support item assignment\r\n>>> S = 'z' + S[1:] # But we can run expressions to make new objects\r\n>>> S\r\n'zpam'<\/pre>\n
Every object in Python is classified as either immutable (unchangeable)<\/em> or not. In terms
\nof the core types, numbers<\/em>, strings<\/em>, and tuples<\/em> are immutable; lists<\/em>, dictionaries<\/em>, and
\nsets<\/em> are not\u2014they can be changed in place freely, as can most new objects you\u2019ll code
\nwith classes.<\/p>\n
Strictly speaking, you can change text-based data in place if you either expand it into a
\nlist of individual characters and join it back together with nothing between, or use the
\nnewer bytearray type available in Pythons 2.6, 3.0, and later:<\/p>\n
>>> S = 'shrubbery'\r\n>>> L = list(S) # Expand to a list: [...]\r\n>>> L\r\n['s', 'h', 'r', 'u', 'b', 'b', 'e', 'r', 'y']\r\n>>> L[1] = 'c' # Change it in place\r\n>>> ''.join(L) # Join with empty delimiter\r\n'scrubbery'\r\n>>> B = bytearray(b'spam') # A bytes\/list hybrid (ahead)\r\n>>> B.extend(b'eggs') # 'b' needed in 3.X, not 2.X\r\n>>> B # B[i] = ord(c) works here too\r\nbytearray(b'spameggs')\r\n>>> B.decode() # Translate to normal string\r\n'spameggs'<\/pre>\n
Type-Specific Methods<\/h4>\n
For example, the string find method is the basic substring search operation (it returns
\nthe offset of the passed-in substring, or \u22121 if it is not present), and the string replace
\nmethod performs global searches and replacements; both act on the subject that they
\nare attached to and called from:<\/p>\n
>>> S = 'Spam'\r\n>>> S.find('pa') # Find the offset of a substring in S\r\n1\r\n>>> S\r\n'Spam'\r\n>>> S.replace('pa', 'XYZ') # Replace occurrences of a string in S with another\r\n'SXYZm'\r\n>>> S\r\n'Spam'<\/pre>\n
>> line = 'aaa,bbb,ccccc,dd'\r\n>>> line.split(',') # Split on a delimiter into a list of substrings\r\n['aaa', 'bbb', 'ccccc', 'dd']\r\n>>> S = 'spam'\r\n>>> S.upper() # Upper- and lowercase conversions\r\n'SPAM'\r\n>>> S.isalpha() # Content tests: isalpha, isdigit, etc.\r\nTrue\r\n>>> line = 'aaa,bbb,ccccc,dd\\n'\r\n>>> line.rstrip() # Remove whitespace characters on the right side\r\n'aaa,bbb,ccccc,dd'\r\n>>> line.rstrip().split(',') # Combine two operations\r\n['aaa', 'bbb', 'ccccc', 'dd']<\/pre>\n
Notice the last command here\u2014it strips before it splits because Python runs from left
\nto right, making a temporary result along the way. Strings also support an advanced
\nsubstitution operation known as formatting, available as both an expression (the original)
\nand a string method call (new as of 2.6 and 3.0); the second of these allows you
\nto omit relative argument value numbers as of 2.7 and 3.1:<\/p>\n
>> '%s, eggs, and %s' % ('spam', 'SPAM!') # Formatting expression (all)\r\n'spam, eggs, and SPAM!'\r\n>>> '{0}, eggs, and {1}'.format('spam', 'SPAM!') # Formatting method (2.6+, 3.0+)\r\n'spam, eggs, and SPAM!'\r\n>>> '{}, eggs, and {}'.format('spam', 'SPAM!') # Numbers optional (2.7+, 3.1+)\r\n'spam, eggs, and SPAM!'<\/pre>\n
Formatting is rich with features, which we\u2019ll postpone discussing until later in this
\nbook, and which tend to matter most when you must generate numeric reports:<\/p>\n
>>> '{:,.2f}'.format(296999.2567) # Separators, decimal digits\r\n'296,999.26'\r\n>>> '%.2f | %+05d' % (3.14159, \u221242) # Digits, padding, signs\r\n'3.14 | \u22120042'<\/pre>\n
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\u0412\u0441\u0442\u0440\u043e\u0435\u043d\u043d\u044b\u0435 \u043e\u0431\u044a\u0435\u043a\u0442\u044b Object type Example literals\/creation Numbers 1234, 3.1415, 3+4j, 0b111, Decimal(), Fraction() Strings ‘spam’, “Bob’s”, b’a\\x01c’, u’sp\\xc4m’ Lists [1, [2, ‘three’], 4.5], list(range(10)) Dictionaries {‘food’: ‘spam’, ‘taste’: ‘yum’}, dict(hours=10) Tuples (1, ‘spam’, 4, ‘U’), tuple(‘spam’), namedtuple Files open(‘eggs.txt’), open(r’C:\\ham.bin’, ‘wb’) Sets set(‘abc’), {‘a’, ‘b’, ‘c’} Other core types Booleans, types, None Numbers >>> 123 …<\/p>\n
Continue reading ‘Python3’ »<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-4875","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/tst-amo.net.ua\/blog\/index.php?rest_route=\/wp\/v2\/posts\/4875"}],"collection":[{"href":"https:\/\/tst-amo.net.ua\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tst-amo.net.ua\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tst-amo.net.ua\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/tst-amo.net.ua\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4875"}],"version-history":[{"count":16,"href":"https:\/\/tst-amo.net.ua\/blog\/index.php?rest_route=\/wp\/v2\/posts\/4875\/revisions"}],"predecessor-version":[{"id":4895,"href":"https:\/\/tst-amo.net.ua\/blog\/index.php?rest_route=\/wp\/v2\/posts\/4875\/revisions\/4895"}],"wp:attachment":[{"href":"https:\/\/tst-amo.net.ua\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4875"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tst-amo.net.ua\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4875"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tst-amo.net.ua\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4875"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}