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Lesson 4 Strings

Pragmatic AI Labs

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4.1 Use string methods

String Quoting

Single quotes

'Here is a string'

'Here is a string'

Double quotes

"Here is a string" == 'Here is a string'

True

Triple Strings

a_very_large_phrase = """
Wikipedia is hosted by the Wikimedia Foundation, 
a non-profit organization that also hosts a range of other projects.
"""

print(a_very_large_phrase)


Wikipedia is hosted by the Wikimedia Foundation, 
a non-profit organization that also hosts a range of other projects.

Raw Strings

jon_jones = '...wrote on twitter he is the greatest "heavyw8e! \nfighter of all time'
print(jon_jones)

...wrote on twitter he is the greatest "heavyw8e! 
fighter of all time


jon_jones = r'...wrote on twitter he is the greatest "heavyw8e! \nfighter of all time'
print(jon_jones)

...wrote on twitter he is the greatest "heavyw8e! \nfighter of all time

Case Manipulation

captain = "Patrick Tayluer"

captain

'Patrick Tayluer'

captain.capitalize()

'Patrick tayluer'

captain.lower()

'patrick tayluer'

captain.upper()

'PATRICK TAYLUER'

captain.swapcase()

'pATRICK tAYLUER'

captain = 'patrick tayluer'
captain.title()

'Patrick Tayluer'

Interrogation

river = 'Mississippi'


len(river)

11

river.count('s')

4

river.index('pp')

8

river.index('r')


    ---------------------------------------------------------------------------

    ValueError                                Traceback (most recent call last)

    <ipython-input-67-fcd85454de2b> in <module>()
    ----> 1 river.index('r')
    

    ValueError: substring not found



river.find('r')

-1

river.startswith('M')

True

river.endswith('i')

True

'sip' in river

True

Content Type

'abc123'.isalpha()

False

'abc123'.isalnum()

True

'lowercase'.islower()

True

'lowercase'.isupper()

False

'The Good Ship'.istitle()

True

'The bad seed'.istitle()

False

More information: String Methods

4.2 Format strings

F-strings where introduced in Python 3.6. They prefixed by either a ‘F’ or ‘f’ before the beginning quotation mark. Values can be inserted into F-strings at runtime using replacement fields which are deliminated by curly braces.

Insert variable into replacement field

strings_count = 5
frets_count = 24
f"Noam Pikelny's banjo has {strings_count} strings and {frets_count} frets"

"Noam Pikelny's banjo has 5 strings and 24 frets"

Insert expression into replacement field

a = 12
b = 32
f"{a} times {b} equals {a*b}"

'12 times 32 equals 384'

Index list in string replacement fields

players = ["Tony Trischka", "Bill Evans", "Alan Munde"]
f"Performances will be held by {players[1]}, {players[0]}, and {players[2]}"

'Performances will be held by Bill Evans, Tony Trischka, and Alan Munde'

Conversion flags

A conversion flag can be specified to convert the type of the value before formatting. The three available flags are ‘s’, ‘r’ and ‘a’.

Using str conversion

nuts = [1,2,3,4,5]
f"Calling str() on a the list {nuts} produces {nuts!s}"

'Calling str() on a the list [1, 2, 3, 4, 5] produces [1, 2, 3, 4, 5]'

Using repr conversiont

nut = 'pistacio'
f"Calling repr on the string {nut} results in {nut!r}"

"Calling repr on the string pistacio results in 'pistacio'"

Using ascii conversion

check = "√"
f"The ascii version of {check} is {check!a}"

"The ascii version of √ is '\\u221a'"

Padding a number

lucky_num = 13
f"To pad the number {lucky_num} to 5 places:{lucky_num:5d}"

'To pad the number 13 to 5 places:   13'

Setting padding value at runtime

luckey_num = 13
padding = 5
f"To pad the number {lucky_num} to {padding} places:{lucky_num:{padding}d}"

'To pad the number 13 to 5 places:   13'

More information: Format String Syntax

Other String Formatting: String Format Method

Old Style String Formatting

4.3 Manipulate strings

Concatenation

"Bob" + "beroo"

'Bobberoo'

"AB" * 8

'ABABABABABABABAB'

Remove Whitespace

ship = " The Yankee Clipper "
ship

' The Yankee Clipper '

ship.strip()

'The Yankee Clipper'

ship.lstrip()

'The Yankee Clipper '

ship.rstrip()

' The Yankee Clipper'

ship.rstrip("per ")

' The Yankee Cli'

Add padding

port = "Boston"

port.center(12, '*')

'***Boston***'

port.ljust(12, '*')

'Boston******'

port.rjust(12, '*')

'******Boston'

for port_city in ['Liverpool', 'Boston', 'New York', 'Philadelphia']:
  print(port_city.rjust(12))

   Liverpool
      Boston
    New York
Philadelphia


'-5'.zfill(4)

'-005'

Replace

"FILADELFIA".replace("F", "PH")

'PHILADELPHIA'

Spitting and Joining

words_string = "Here,Are,Some,Words"
words_string

'Here,Are,Some,Words'

Split on comma

words = words_string.split(',')
words

['Here', 'Are', 'Some', 'Words']

Joining

':'.join(words)

'Here:Are:Some:Words'

Split on newline

multiline = "Sometimes we are given\na multiline document\nas a single string"
multiline

'Sometimes we are given\na multiline document\nas a single string'

for line in multiline.splitlines():
  print(line)

Sometimes we are given
a multiline document
as a single string

Slicing

collector = "William Main Doerflinger"
collector[0]

'W'

collector[-1]

'r'

collector[13:18]

'Doerf'

collector[-7:]

'flinger'

More information: common sequence operations

4.4 Learn to use unicode

There are multiple encoding possible for mapping characters to bytes. Python strings default to UTF-8. Earlier versions of Python used a more limited encoding.

Encode

twice_pie = 'ππ'
twice_pie

'ππ'

twice_π = twice_pie
twice_π

'ππ'

pie = "\N{GREEK CAPITAL LETTER PI}"
pie

'Π'

ord(pie)

928

chr(928)

'Π'

u = chr(40960) + 'abcd' + chr(1972)
u.encode('utf-8')
u

'ꀀabcd\u07b4'

Saving File in Unicode

with open("new_file.txt", "w", encoding='utf-8') as opened_file:
  opened_file.write("Søme Unˆcode text")
  
!cat new_file.txt
  

Søme Unˆcode text

Unicode

Notes