Регулярные выражения в python: теория и практика

3.2. First Steps Towards Programming¶

Of course, we can use Python for more complicated tasks than adding two and two
together. For instance, we can write an initial sub-sequence of the
Fibonacci series
as follows:

>>> # Fibonacci series:
... # the sum of two elements defines the next
... a, b = , 1
>>> while a < 10
...     print(a)
...     a, b = b, a+b
...

1
1
2
3
5
8

This example introduces several new features.

• The first line contains a multiple assignment: the variables and
  simultaneously get the new values 0 and 1. On the last line this is used again,
  demonstrating that the expressions on the right-hand side are all evaluated
  first before any of the assignments take place. The right-hand side expressions
  are evaluated from the left to the right.

• The loop executes as long as the condition (here: )
  remains true. In Python, like in C, any non-zero integer value is true; zero is
  false. The condition may also be a string or list value, in fact any sequence;
  anything with a non-zero length is true, empty sequences are false. The test
  used in the example is a simple comparison. The standard comparison operators
  are written the same as in C: (less than), (greater than),
  (equal to), (less than or equal to), (greater than or equal to)
  and (not equal to).

• The body of the loop is indented: indentation is Python’s way of grouping
  statements. At the interactive prompt, you have to type a tab or space(s) for
  each indented line. In practice you will prepare more complicated input
  for Python with a text editor; all decent text editors have an auto-indent
  facility. When a compound statement is entered interactively, it must be
  followed by a blank line to indicate completion (since the parser cannot
  guess when you have typed the last line). Note that each line within a basic
  block must be indented by the same amount.

• The function writes the value of the argument(s) it is given.
  It differs from just writing the expression you want to write (as we did
  earlier in the calculator examples) in the way it handles multiple arguments,
  floating point quantities, and strings. Strings are printed without quotes,
  and a space is inserted between items, so you can format things nicely, like
  this:

  >>> i = 256*256
  >>> print('The value of i is', i)
  The value of i is 65536
  

  The keyword argument end can be used to avoid the newline after the output,
  or end the output with a different string:

  >>> a, b = , 1
  >>> while a < 1000
  ...     print(a, end=',')
  ...     a, b = b, a+b
  ...
  0,1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,
  

Footnotes

Since has higher precedence than , will be
interpreted as and thus result in . To avoid this
and get , you can use .

Unlike other languages, special characters such as have the
same meaning with both single () and double () quotes.
The only difference between the two is that within single quotes you don’t
need to escape (but you have to escape ) and vice versa.

defaultdict objects¶

class (default_factory=None, , …)

Регулярные выражения

Return a new dictionary-like object. is a subclass of the
built-in class. It overrides one method and adds one writable
instance variable. The remaining functionality is the same as for the
class and is not documented here.

The first argument provides the initial value for the
attribute; it defaults to . All remaining arguments are treated the same
as if they were passed to the constructor, including keyword
arguments.

objects support the following method in addition to the
standard operations:

(key)

If the attribute is , this raises a
exception with the key as argument.

If is not , it is called without arguments
to provide a default value for the given key, this value is inserted in
the dictionary for the key, and returned.

If calling raises an exception this exception is
propagated unchanged.

This method is called by the method of the
class when the requested key is not found; whatever it
returns or raises is then returned or raised by .

Note that is not called for any operations besides
. This means that will, like normal
dictionaries, return as a default rather than using
.

objects support the following instance variable:

This attribute is used by the method; it is
initialized from the first argument to the constructor, if present, or to
, if absent.

Changed in version 3.9: Added merge () and update () operators, specified in
PEP 584.

4.4. break and continue Statements, and else Clauses on Loops¶

The statement, like in C, breaks out of the innermost enclosing
or loop.

Loop statements may have an clause; it is executed when the loop
terminates through exhaustion of the iterable (with ) or when the
condition becomes false (with ), but not when the loop is
terminated by a statement. This is exemplified by the
following loop, which searches for prime numbers:

>>> for n in range(2, 10):
...     for x in range(2, n):
...         if n % x == 
...             print(n, 'equals', x, '*', n//x)
...             break
...     else
...         # loop fell through without finding a factor
...         print(n, 'is a prime number')
...
2 is a prime number
3 is a prime number
4 equals 2 * 2
5 is a prime number
6 equals 2 * 3
7 is a prime number
8 equals 2 * 4
9 equals 3 * 3

(Yes, this is the correct code. Look closely: the clause belongs to
the loop, not the statement.)

When used with a loop, the clause has more in common with the
clause of a statement than it does with that of
statements: a statement’s clause runs
when no exception occurs, and a loop’s clause runs when no
occurs. For more on the statement and exceptions, see
.

The statement, also borrowed from C, continues with the next
iteration of the loop:

UserList objects¶

This class acts as a wrapper around list objects. It is a useful base class
for your own list-like classes which can inherit from them and override
existing methods or add new ones. In this way, one can add new behaviors to
lists.

The need for this class has been partially supplanted by the ability to
subclass directly from ; however, this class can be easier
to work with because the underlying list is accessible as an attribute.

class (list)

Class that simulates a list. The instance’s contents are kept in a regular
list, which is accessible via the attribute of
instances. The instance’s contents are initially set to a copy of list,
defaulting to the empty list . list can be any iterable, for
example a real Python list or a object.

In addition to supporting the methods and operations of mutable sequences,
instances provide the following attribute:

A real object used to store the contents of the
class.

Subclassing requirements: Subclasses of are expected to
offer a constructor which can be called with either no arguments or one
argument. List operations which return a new sequence attempt to create an
instance of the actual implementation class. To do so, it assumes that the
constructor can be called with a single parameter, which is a sequence object
used as a data source.

Sets

A set is a set of characters inside a pair of square brackets with a special meaning:

4.9. Intermezzo: Coding Style¶

Now that you are about to write longer, more complex pieces of Python, it is a
good time to talk about coding style. Most languages can be written (or more
concise, formatted) in different styles; some are more readable than others.
Making it easy for others to read your code is always a good idea, and adopting
a nice coding style helps tremendously for that.

For Python, PEP 8 has emerged as the style guide that most projects adhere to;
it promotes a very readable and eye-pleasing coding style. Every Python
developer should read it at some point; here are the most important points
extracted for you:

• Use 4-space indentation, and no tabs.

  4 spaces are a good compromise between small indentation (allows greater
  nesting depth) and large indentation (easier to read). Tabs introduce
  confusion, and are best left out.

• Wrap lines so that they don’t exceed 79 characters.

  This helps users with small displays and makes it possible to have several
  code files side-by-side on larger displays.

• Use blank lines to separate functions and classes, and larger blocks of
  code inside functions.

• When possible, put comments on a line of their own.

• Use docstrings.

• Use spaces around operators and after commas, but not directly inside
  bracketing constructs: .

• Name your classes and functions consistently; the convention is to use
  for classes and for functions
  and methods. Always use as the name for the first method argument
  (see for more on classes and methods).

• Don’t use fancy encodings if your code is meant to be used in international
  environments. Python’s default, UTF-8, or even plain ASCII work best in any
  case.

• Likewise, don’t use non-ASCII characters in identifiers if there is only the
  slightest chance people speaking a different language will read or maintain
  the code.

Footnotes

Actually, call by object reference would be a better description,
since if a mutable object is passed, the caller will see any changes the
callee makes to it (items inserted into a list).

Основные регулярные выражения

re.match() – ищет совпадения в тексте, по умолчанию в начале строки.

import re

pattern = ‘34’
testString = ’12 timeweb 34 community 58’
result = re.search(pattern, testString)

print(result)
# Результат None, если совпадения будут обнаружены - result вернет их.

re.findall() – возвращает все строки, где было обнаружено совпадение.

import re

pattern = ‘\d+’ (ищем только числа с помощью метасимволов, об этом далее)
testString = ’12 timeweb 34 community 58’
result = re.findall(pattern, testString)

print(result)
# Результат , если совпадения не будут обнаружены - то []

re.split() – разбивает строки по заданному паттерну и возвращает разбитые строки.

import re

pattern = ‘\d+’
testString = ’12 timeweb 34 community 58’
result = re.split(pattern, testString)

print(result)
# Результат , если совпадения не будут обнаружены - то []

re.sub() – заменяет символы по заданному паттерну на заданные символы и возвращает исправленную строку.

import re

pattern = ‘timeweb’
replace = ‘hello’
testString = ’timeweb community of timeweb community’
result = re.sub(pattern, replace, testString)

print(result)
# Результат ‘hello community of hello community’, если совпадения не будут обнаружены, то вернется первоначальная строка.

re.search() – ищет указанный паттерн в строке и при первом же совпадении возвращает сам паттерн, в ином же случае возвращает None. 

import re

pattern = ‘34’
testString = ’12 timeweb 34 community 58’
result = re.search(pattern, testString)

print(result)
# Результат ‘34’, если совпадения не будут обнаружены - None.

Шаблон регулярного выражения

Строка шаблона, используя специальный синтаксис для обозначения регулярное выражение:

Буквы и цифры сами. Регулярное выражение при букв и цифр совпадают ту же строку.

Большинство из букв и цифр будет иметь различное значение, когда ему предшествует обратный слэш.

Пунктуация спасшемся только тогда, когда сам матч, или они представляют собой особый смысл.

Сам Backslash должен использовать побег символ обратной косой.

Поскольку регулярные выражения обычно содержат символы, так что вам лучше использовать исходную строку, чтобы представлять их. Элементы схемы (например, г ‘/ т’, что эквивалентно ‘// Т’) совпадает с соответствующим специальные символы.

В следующей таблице перечислены синтаксис регулярных выражений шаблон конкретных элементов. Если ваши модели использования, обеспечивая при этом необязательные флаги аргумент, значение некоторых элементов рисунка будет меняться.

[Коллекция] Каковы различные квантификаторы Python Re?

Если вы хотите использовать (и понимать) регулярные выражения на практике, вам нужно знать самые важные квантования, которые могут быть применены к любому Regeex (включая Regex dotex)!

Так что давайте погрузимся в другие регеисы:

Квантификатор
Описание
Пример
.
Wild-Card («DOT») соответствует любому символу в строке, кроме нового символа «\ N».
Regex ‘…’ соответствует всем словам с тремя символами, такими как «abc», «Cat» и «собака».
*
Звездочка нулевой или больше соответствует произвольному количеству вхождений (включая нулевые вхождения) непосредственно предшествующего Regex.
Regex ‘Cat *’ соответствует строкам «CA», «CAT», «CATT», «CATTT» и «CATTTTTTT». —
?
Матчи ноль или один (как следует из названия) либо ноль, либо в одних случаях непосредственно предшествующего Regex.
Regex ‘Cat?’ Соответствует обеим струнам «Ca» и «CAT» – но не «CATT», «CATTT» и «CATTTTTTT».
+
По меньшей мере, один соответствует одному или нескольким вхождению непосредственно предшествующего регеек.
Regex ‘Cat +’ не соответствует строке «CA», а соответствует всем строкам, по меньшей мере, одним задним характером «T», такими как «кошка», «CATT» и «CATTT».
^
Начальная строка соответствует началу строки.
Regex ‘^ p’ соответствует строкам «Python» и «программирование», но не «Lisp» и «шпионить», где символ «p» не происходит в начале строки.
$
Конец строки соответствует концу строки.
Regex ‘Py $’ будет соответствовать строкам «Main.py» и «Pypy», но не строки «Python» и «pypi».
A | B.
Или соответствует либо регезе A или REGEX B

Обратите внимание, что интуиция сильно отличается от стандартной интерпретации или оператора, который также может удовлетворить оба условия.
Regex ‘(Hello) | (Привет) «Соответствует строки« Hello World »и« Привет Python ». Было бы не иметь смысла попытаться сопоставить их обоих одновременно.
Аб
И совпадает с первым регелем А и второе регулярное выражение в этой последовательности.
Мы уже видели его тривиально в Regex ‘Ca’, которое соответствует первым Regex ‘C’ и Second Regex ‘A’.

Обратите внимание, что я дал вышеупомянутые операторы некоторых более значимых имен (жирным шрифтом), чтобы вы могли немедленно понять цель каждого Regex. Например, Оператор обычно обозначается как оператор «Caret»

Эти имена не описаны Поэтому я придумал более детские сады, такие как оператор «Пусковая строка».

Мы уже видели много примеров, но давайте погрузимся еще больше!

import re

text = '''
    Ha! let me see her: out, alas! he's cold:
    Her blood is settled, and her joints are stiff;
    Life and these lips have long been separated:
    Death lies on her like an untimely frost
    Upon the sweetest flower of all the field.
'''

print(re.findall('.a!', text))
'''
Finds all occurrences of an arbitrary character that is
followed by the character sequence 'a!'.

'''

print(re.findall('is.*and', text))
'''
Finds all occurrences of the word 'is',
followed by an arbitrary number of characters
and the word 'and'.

'''

print(re.findall('her:?', text))
'''
Finds all occurrences of the word 'her',
followed by zero or one occurrences of the colon ':'.

'''

print(re.findall('her:+', text))
'''
Finds all occurrences of the word 'her',
followed by one or more occurrences of the colon ':'.

'''


print(re.findall('^Ha.*', text))
'''
Finds all occurrences where the string starts with
the character sequence 'Ha', followed by an arbitrary
number of characters except for the new-line character. 
Can you figure out why Python doesn't find any?
[]
'''

print(re.findall('n$', text))
'''
Finds all occurrences where the new-line character 'n'
occurs at the end of the string.

'''

print(re.findall('(Life|Death)', text))
'''
Finds all occurrences of either the word 'Life' or the
word 'Death'.

'''

В этих примерах вы уже видели специальный символ который обозначает нового стилевого символа в Python (и большинство других языках). Есть много специальных символов, специально предназначенных для регулярных выражений.

This is the tenth and final regular maintenance release of Python 3.8

Note: The release you’re looking at is Python 3.8.10, a bugfix release for the legacy 3.8 series. Python 3.9 is now the latest feature release series of Python 3. Get the latest release of 3.9.x here.

According to the release calendar specified in PEP 569, Python 3.8.10 is the final regular maintenance release. Starting now, the 3.8 branch will only accept security fixes and releases of those will be made in source-only form until October 2024.

Compared to the 3.7 series, this last regular bugfix release is relatively dormant at 92 commits since 3.8.9. Version 3.7.8, the final regular bugfix release of Python 3.7, included 187 commits. But there’s a bunch of important updates here regardless, the biggest being Big Sur and Apple Silicon build support. This work would not have been possible without the effort of Ronald Oussoren, Ned Deily, Maxime Bélanger, and Lawrence D’Anna from Apple. Thank you!

Take a look at the change log for details.

Major new features of the 3.9 series, compared to 3.8

Some of the new major new features and changes in Python 3.9 are:

• PEP 573, Module State Access from C Extension Methods
• PEP 584, Union Operators in
• PEP 585, Type Hinting Generics In Standard Collections
• PEP 593, Flexible function and variable annotations
• PEP 602, Python adopts a stable annual release cadence
• PEP 614, Relaxing Grammar Restrictions On Decorators
• PEP 615, Support for the IANA Time Zone Database in the Standard Library
• PEP 616, String methods to remove prefixes and suffixes
• PEP 617, New PEG parser for CPython
• BPO 38379, garbage collection does not block on resurrected objects;
• BPO 38692, os.pidfd_open added that allows process management without races and signals;
• BPO 39926, Unicode support updated to version 13.0.0;
• BPO 1635741, when Python is initialized multiple times in the same process, it does not leak memory anymore;
• A number of Python builtins (range, tuple, set, frozenset, list, dict) are now sped up using PEP 590 vectorcall;
• A number of Python modules (_abc, audioop, _bz2, _codecs, _contextvars, _crypt, _functools, _json, _locale, operator, resource, time, _weakref) now use multiphase initialization as defined by PEP 489;
• A number of standard library modules (audioop, ast, grp, _hashlib, pwd, _posixsubprocess, random, select, struct, termios, zlib) are now using the stable ABI defined by PEP 384.

You can find a more comprehensive list in this release’s «What’s New» document.

macOS users

• For Python 3.8, we provide one installer: 64-bit-only that works on macOS 10.9 (Mavericks) and later systems.
• Please read the «Important Information» displayed during installation for information about SSL/TLS certificate validation and the running the «Install Certificates.command».

Major new features of the 3.9 series, compared to 3.8

Some of the new major new features and changes in Python 3.9 are:

• PEP 573, Module State Access from C Extension Methods
• PEP 584, Union Operators in
• PEP 585, Type Hinting Generics In Standard Collections
• PEP 593, Flexible function and variable annotations
• PEP 602, Python adopts a stable annual release cadence
• PEP 614, Relaxing Grammar Restrictions On Decorators
• PEP 615, Support for the IANA Time Zone Database in the Standard Library
• PEP 616, String methods to remove prefixes and suffixes
• PEP 617, New PEG parser for CPython
• BPO 38379, garbage collection does not block on resurrected objects;
• BPO 38692, os.pidfd_open added that allows process management without races and signals;
• BPO 39926, Unicode support updated to version 13.0.0;
• BPO 1635741, when Python is initialized multiple times in the same process, it does not leak memory anymore;
• A number of Python builtins (range, tuple, set, frozenset, list, dict) are now sped up using PEP 590 vectorcall;
• A number of Python modules (_abc, audioop, _bz2, _codecs, _contextvars, _crypt, _functools, _json, _locale, operator, resource, time, _weakref) now use multiphase initialization as defined by PEP 489;
• A number of standard library modules (audioop, ast, grp, _hashlib, pwd, _posixsubprocess, random, select, struct, termios, zlib) are now using the stable ABI defined by PEP 384.

You can find a more comprehensive list in this release’s «What’s New» document.

Примеры Re.findall ()

Импорт Модуль и создайте текстовую строку для поиска шаблонов Regex:

import re

text = '''
    Ha! let me see her: out, alas! he's cold:
    Her blood is settled, and her joints are stiff;
    Life and these lips have long been separated:
    Death lies on her like an untimely frost
    Upon the sweetest flower of all the field.
'''

Допустим, вы хотите найти текст для строки :

>>> re.findall('her', text)

Первый аргумент – это шаблон, который вы ищете. В нашем случае это строка Отказ Второй аргумент – это текст, который будет проанализирован. Вы сохранили многострочную строку в переменной — Поэтому вы принимаете это как второй аргумент. Вам не нужно определять дополнительный третий аргумент из Способ, потому что вы в порядке с поведением по умолчанию в этом случае.

Также обратите внимание, что Функция Возвращает список всех совпадающих подстроек. В этом случае это может быть не слишком полезно, потому что мы ищите только точную строку

Но если мы ищем более сложные шаблоны, это может быть действительно очень полезно:

>>> re.findall('\\bf\w+\\b', text)

Regex Соответствует всем словам, которые начинаются с персонажа Отказ

Вы можете спросить: зачем приложить Regex с ведущим и трейлинговым ? Это граничный символ слова, который соответствует пустой строке в начале или в конце слова. Вы можете определить слово как последовательность символов, которые не являются персонажами пробелов или другие разделители, такие как .

В предыдущем примере вам нужно избежать границы символа Опять же, потому что в строке Python отображение по умолчанию последовательность символов это символ обратной косания.

Examples¶

Basic examples:

>>> random()                             # Random float:  0.0 <= x < 1.0
0.37444887175646646

>>> uniform(2.5, 10.0)                   # Random float:  2.5 <= x <= 10.0
3.1800146073117523

>>> expovariate(1  5)                   # Interval between arrivals averaging 5 seconds
5.148957571865031

>>> randrange(10)                        # Integer from 0 to 9 inclusive
7

>>> randrange(, 101, 2)                 # Even integer from 0 to 100 inclusive
26

>>> choice()      # Single random element from a sequence
'draw'

>>> deck = 'ace two three four'.split()
>>> shuffle(deck)                        # Shuffle a list
>>> deck


>>> sample(, k=4)    # Four samples without replacement

Simulations:

>>> # Six roulette wheel spins (weighted sampling with replacement)
>>> choices(, 18, 18, 2], k=6)


>>> # Deal 20 cards without replacement from a deck
>>> # of 52 playing cards, and determine the proportion of cards
>>> # with a ten-value:  ten, jack, queen, or king.
>>> dealt = sample(, counts=16, 36], k=20)
>>> dealt.count('tens')  20
0.15

>>> # Estimate the probability of getting 5 or more heads from 7 spins
>>> # of a biased coin that settles on heads 60% of the time.
>>> def trial():
...     return choices('HT', cum_weights=(0.60, 1.00), k=7).count('H') >= 5
...
>>> sum(trial() for i in range(10_000))  10_000
0.4169

>>> # Probability of the median of 5 samples being in middle two quartiles
>>> def trial():
...     return 2_500 <= sorted(choices(range(10_000), k=5))[2 < 7_500
...
>>> sum(trial() for i in range(10_000))  10_000
0.7958

Example of statistical bootstrapping using resampling
with replacement to estimate a confidence interval for the mean of a sample:

# http://statistics.about.com/od/Applications/a/Example-Of-Bootstrapping.htm
from statistics import fmean as mean
from random import choices

data = 41, 50, 29, 37, 81, 30, 73, 63, 20, 35, 68, 22, 60, 31, 95
means = sorted(mean(choices(data, k=len(data))) for i in range(100))
print(f'The sample mean of {mean(data).1f} has a 90% confidence '
      f'interval from {means5.1f} to {means94.1f}')

Example of a
to determine the statistical significance or p-value of an observed difference
between the effects of a drug versus a placebo:

# Example from "Statistics is Easy" by Dennis Shasha and Manda Wilson
from statistics import fmean as mean
from random import shuffle

drug = 54, 73, 53, 70, 73, 68, 52, 65, 65
placebo = 54, 51, 58, 44, 55, 52, 42, 47, 58, 46
observed_diff = mean(drug) - mean(placebo)

n = 10_000
count = 
combined = drug + placebo
for i in range(n):
    shuffle(combined)
    new_diff = mean(combined) - mean(combinedlen(drug):])
    count += (new_diff >= observed_diff)

print(f'{n} label reshufflings produced only {count} instances with a difference')
print(f'at least as extreme as the observed difference of {observed_diff.1f}.')
print(f'The one-sided p-value of {count  n.4f} leads us to reject the null')
print(f'hypothesis that there is no difference between the drug and the placebo.')

Simulation of arrival times and service deliveries for a multiserver queue:

from heapq import heapify, heapreplace
from random import expovariate, gauss
from statistics import mean, quantiles

average_arrival_interval = 5.6
average_service_time = 15.0
stdev_service_time = 3.5
num_servers = 3

waits = []
arrival_time = 0.0
servers = 0.0 * num_servers  # time when each server becomes available
heapify(servers)
for i in range(1_000_000):
    arrival_time += expovariate(1.0  average_arrival_interval)
    next_server_available = servers
    wait = max(0.0, next_server_available - arrival_time)
    waits.append(wait)
    service_duration = max(0.0, gauss(average_service_time, stdev_service_time))
    service_completed = arrival_time + wait + service_duration
    heapreplace(servers, service_completed)

print(f'Mean wait: {mean(waits).1f}   Max wait: {max(waits).1f}')
print('Quartiles:', round(q, 1) for q in quantiles(waits)])

This is the ninth maintenance release of Python 3.8

Note: The release you’re looking at is Python 3.8.9, a bugfix release for the legacy 3.8 series. Python 3.9 is now the latest feature release series of Python 3. Get the latest release of 3.9.x here.

3.8.9 is an expedited release which includes a number of security fixes and is recommended to all users:

• bpo-43631: high-severity CVE-2021-3449 and CVE-2021-3450 were published for OpenSSL, it’s been upgraded to 1.1.1k in CI, and macOS and Windows installers.
• bpo-42988: CVE-2021-3426: Remove the getfile feature of the pydoc module which could be abused to read arbitrary files on the disk (directory traversal vulnerability). Moreover, even source code of Python modules can contain sensitive data like passwords. Vulnerability reported by David Schwörer.
• bpo-43285: ftplib no longer trusts the IP address value returned from the server in response to the PASV command by default. This prevents a malicious FTP server from using the response to probe IPv4 address and port combinations on the client network. Code that requires the former vulnerable behavior may set a trust_server_pasv_ipv4_address attribute on their ftplib.FTP instances to True to re-enable it.
• bpo-43439: Add audit hooks for gc.get_objects(), gc.get_referrers() and gc.get_referents(). Patch by Pablo Galindo.