9.3. Syntax Anchor

  • . - any character except a newline (changes meaning with re.DOTALL)

  • ^ - start of line (changes meaning with re.MULTILINE)

  • $ - end of line (changes meaning with re.MULTILINE)

  • \A - start of text (doesn't change meaning with re.MULTILINE)

  • \Z - end of text (doesn't change meaning with re.MULTILINE)

9.3.1. Any Character

  • . - any character except a newline (changes meaning with re.DOTALL)

>>> import re
>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

Search for letters No followed by any character:

>>> re.findall(r'No.', TEXT)
['Nov']

Search for uppercase letter followed by any three characters:

>>> re.findall(r'[A-Z]...', TEXT)
['Mark', 'Watn', 'Ares', 'Mars', 'Nov ']

Example:

>>> re.findall(r'1:37 ..', TEXT)
['1:37 pm']
>>>
>>> re.findall(r'Nov 7..', TEXT)
['Nov 7th']

9.3.2. Start of Line

  • ^ - start of a line

  • Changes meaning with re.MULTILINE

>>> import re
>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

Search for a capital letter in text at the start of a line:

>>> re.findall(r'^[A-Z]', TEXT)
['M']

Search for a capital letter anywhere in text:

>>> re.findall(r'[A-Z]', TEXT)
['M', 'W', 'A', 'M', 'N']

9.3.3. End of Line

  • $ - end of line

  • Changes meaning with re.MULTILINE

>>> import re
>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

Give me last two characters in a text:

>>> re.findall(r'..$', TEXT)
['pm']

9.3.4. Start of String

  • \A - start of a text

  • Doesn't change meaning with re.MULTILINE

>>> import re
>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

Search for a capital letter in text at the start of a line:

>>> re.findall(r'\A[A-Z]', TEXT)
['M']

Note, that the output is identical to Start of a Line ^. It will differ when re.MULTILINE flag is present.

>>> re.findall(r'^[A-Z]', TEXT)
['M']

9.3.5. End of String

  • \Z - end of a text

  • Doesn't change meaning with re.MULTILINE

>>> import re
>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

Give me last two characters in a text:

>>> re.findall(r'..\Z', TEXT)
['pm']

Note, that the output is identical to Start of a Line ^. It will differ when re.MULTILINE flag is present.

>>> re.findall(r'..$', TEXT)
['pm']

9.3.6. Use Case - 0x01

  • abc.e - text abc then any character followed by letter e

9.3.7. Assignments

Code 9.11. Solution
"""
* Assignment: RE Syntax Anchor
* Complexity: easy
* Lines of code: 2 lines
* Time: 3 min

English:
    1. Use regular expressions find in text:
        a. uppercase letter at the beginning of a text
        b. uppercase letter at the beginning of each line
    2. Run doctests - all must succeed

Polish:
    1. Użyj wyrażeń regularnych wyszukiwania w tekście:
        a. wielkie litery na początku tekstu
        b. wielkie litery na początku każdej linii
    2. Uruchom doctesty - wszystkie muszą się powieść

Hint:
    * `re.findall()`

References:
    [1] Authors: Wikipedia contributors
        Title: Apollo 11
        Publisher: Wikipedia
        Year: 2019
        Retrieved: 2019-12-14
        URL: https://en.wikipedia.org/wiki/Apollo_11

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from pprint import pprint

    >>> pprint(result_a, compact=True)
    ['A']

    >>> pprint(result_b, compact=True)
    ['A', 'J', 'T', 'B', 'M', 'C']
"""

import re

TEXT = """Apollo 11 was the American spaceflight that first landed
humans on the Moon. Commander (CDR) Neil Armstrong and lunar module
pilot (LMP) Buzz Aldrin landed the Apollo Lunar Module (LM) Eagle on
July 20th, 1969 at 20:17 UTC, and Armstrong became the first person
to step (EVA) onto the Moon's surface (EVA) 6 hours 39 minutes later,
on July 21st, 1969 at 02:56:15 UTC. Aldrin joined him 19 minutes later.
They spent 2 hours 31 minutes exploring the site they had named Tranquility
Base upon landing. Armstrong and Aldrin collected 47.5 pounds (21.5 kg)
of lunar material to bring back to Earth as pilot Michael Collins (CMP)
flew the Command Module (CM) Columbia in lunar orbit, and were on the
Moon's surface for 21 hours 36 minutes before lifting off to rejoin
Columbia."""

# Find uppercase letter at the beginning of a text
# Example: 'A'
# type: list[str]
result_a = ...

# Find uppercase letter at the beginning of each line
# Example: 'A', 'J', 'T', 'B', 'M', 'C'
# type: list[str]
result_b = ...

Code 9.12. Solution
"""
* Assignment: RE Syntax Anchor
* Complexity: easy
* Lines of code: 2 lines
* Time: 3 min

English:
    1. Use regular expressions find in text:
        a. any character at the beginning of a text
        b. any character at the beginning of each line
    2. Run doctests - all must succeed

Polish:
    1. Użyj wyrażeń regularnych wyszukiwania w tekście:
        a. dowolny znak na początku tekstu
        b. dowolny znak na początku każdej linii
    2. Uruchom doctesty - wszystkie muszą się powieść

Hint:
    * `re.findall()`

References:
    [1] Authors: Wikipedia contributors
        Title: Apollo 11
        Publisher: Wikipedia
        Year: 2019
        Retrieved: 2019-12-14
        URL: https://en.wikipedia.org/wiki/Apollo_11

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from pprint import pprint

    >>> pprint(result_a, compact=True)
    ['A']

    >>> pprint(result_b, compact=True)
    ['A', 'h', 'p', 'J', 't', 'o', 'T', 'B', 'o', 'f', 'M', 'C']
"""

import re

TEXT = """Apollo 11 was the American spaceflight that first landed
humans on the Moon. Commander (CDR) Neil Armstrong and lunar module
pilot (LMP) Buzz Aldrin landed the Apollo Lunar Module (LM) Eagle on
July 20th, 1969 at 20:17 UTC, and Armstrong became the first person
to step (EVA) onto the Moon's surface (EVA) 6 hours 39 minutes later,
on July 21st, 1969 at 02:56:15 UTC. Aldrin joined him 19 minutes later.
They spent 2 hours 31 minutes exploring the site they had named Tranquility
Base upon landing. Armstrong and Aldrin collected 47.5 pounds (21.5 kg)
of lunar material to bring back to Earth as pilot Michael Collins (CMP)
flew the Command Module (CM) Columbia in lunar orbit, and were on the
Moon's surface for 21 hours 36 minutes before lifting off to rejoin
Columbia."""

# Find any character at the beginning of a text
# Example: 'A'
# type: list[str]
result_a = ...

# Find any character at the beginning of each line
# Example: 'A', 'h', 'p', 'J', 't', 'o', 'T', 'B', 'o', 'f', 'M', 'C'
# type: list[str]
result_b = ...

Code 9.13. Solution
"""
* Assignment: RE Syntax Anchor
* Complexity: easy
* Lines of code: 2 lines
* Time: 3 min

English:
    1. Use regular expressions find in text:
        a. any character at the end of a text
        b. any character at the end of each line
    2. Run doctests - all must succeed

Polish:
    1. Użyj wyrażeń regularnych wyszukiwania w tekście:
        a. dowolny znak na końcu tekstu
        b. dowolny znak na końcu każdej linii
    2. Uruchom doctesty - wszystkie muszą się powieść

Hint:
    * `re.findall()`

References:
    [1] Authors: Wikipedia contributors
        Title: Apollo 11
        Publisher: Wikipedia
        Year: 2019
        Retrieved: 2019-12-14
        URL: https://en.wikipedia.org/wiki/Apollo_11

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from pprint import pprint

    >>> pprint(result_a, compact=True)
    ['.']

    >>> pprint(result_b, compact=True)
    ['d', 'e', 'n', 'n', ',', '.', 'y', ')', ')', 'e', 'n', '.']
"""

import re

TEXT = """Apollo 11 was the American spaceflight that first landed
humans on the Moon. Commander (CDR) Neil Armstrong and lunar module
pilot (LMP) Buzz Aldrin landed the Apollo Lunar Module (LM) Eagle on
July 20th, 1969 at 20:17 UTC, and Armstrong became the first person
to step (EVA) onto the Moon's surface (EVA) 6 hours 39 minutes later,
on July 21st, 1969 at 02:56:15 UTC. Aldrin joined him 19 minutes later.
They spent 2 hours 31 minutes exploring the site they had named Tranquility
Base upon landing. Armstrong and Aldrin collected 47.5 pounds (21.5 kg)
of lunar material to bring back to Earth as pilot Michael Collins (CMP)
flew the Command Module (CM) Columbia in lunar orbit, and were on the
Moon's surface for 21 hours 36 minutes before lifting off to rejoin
Columbia."""

# Find any character at the end of a text
# Example: '.'
# type: list[str]
result_a = ...

# Find any character at the end of each line
# Example: 'd', 'e', 'n', 'n', ',', '.', 'y', ')', ')', 'e', 'n', '.'
# type: list[str]
result_b = ...