The STR string

• str
• Escape character
• formatting
• Built-in functions

string

• Presentation of text information
• Put it in single, double, triple quotation marks

s = 'I love '
print(s)
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I love 
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s = "I love "
print(s)
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I love 
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s = """
I
Love
"""

print(s)
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I
Love
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Escape character

• A special way to represent a series of inconvenient contents, such as a return key, a newline character, or a backspace key
• With the help of the backslash character, once a backslash appears in the string, one or more characters after the backslash indicate that the meaning is no longer the original, and is escaped
• Be careful when backslashes occur in strings, as there may be escape characters
• Different systems have different representations of newlines
  • Windows: \ n
  • Linux: \ r \ n

# Escape character cases
Let's Go
# Use escape characters
s = 'Let\'s Go'
print(s)


# Use single and double quotation marks
s = "Let's Go"
print(s)

# indicates a slash
For example, C:\User\Augsnano
s = "C:\\User\\Augsnano"
print(s)

# Enter newline
# Intended effect is:
# I
# Love
# You
\r\n can also be used on Windows with the same effect
s = "I\r\nLove\r\nYou"
print(s)
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Let's Go
Let's Go
C:\User\Augsnano
I
Love
You
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Commonly used escape characters

Escape character description (at the end of a line) continuation character (at the end of a line) continuation character (at the end of a line) backslash character (at the end of a line) continuation character (at the end of a line) backslash character (at the end of a line) single quotation mark (at the end of a line) double quotation mark (at the end of a line) DOUBLE quotation mark (at the end of a line) DOUBLE quotation mark (at the end of a line) DOUBLE quotation mark (at the end of a line) double quotation mark (at the end of a line) double quotation mark (at the end of a line) double quotation mark (at the end of a line Octal number, yy for the character, for example: \o12 for newline \xyy hexadecimal, yy for the character. For example: \x0a means newline \other other characters are printed in plain formatCopy the code

# single slash
# In Python, a single backslash indicates an unfinished line, which should continue on the next line for aesthetic reasons
Def maDemo (int x, int y, int z):
def maDemo(x, \ y, \ z) :
    print("hahahahaha")
    
maDemo(1.2.3)
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hahahahaha
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formatting

• To print or fill a string in a format
• Classification of formatting:
  • Traditional formatting
  • format

# fill
s = "I love you"
print(s)

s = "I love you"
print(s)

s = "I love you"
print(s)
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I love you
I love you
I love you
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Traditional formatting of strings

• Format with %

• % (percent sign) is also called a placeholder

  %s: string %r: string, but using repr instead of STR %c: integer converted to a single character % D: decimal integer % U: unsigned integer % O: octal %x: hexadecimal, lowercase letters (x is lowercase) %x: %e: floating point number (e is lowercase), for example, 2.87e+12 %e: floating point number (e is uppercase), for example, 2.87e+12 %f,% f: floating point number in decimal format %g,% g: Decimal floating-point or exponential floating-point automatic conversion Format characters are preceded by an integer to indicate the width of the position occupied by the character. Format characters are preceded by a '-' to indicate left alignment. Format characters are preceded by a '+' to indicate right alignmentCopy the code

# %s represents a simple string
# Placeholders can be used separately
s = "I love %s"
print(s)

s = "I love %s"
print(s%"you")

print(s%"ss")
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I love %s
I love you
I love ss
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print("I love %s"%"you")
Placeholders can generally only be replaced by the same type, or the replacement type can be converted to the type of the placeholder
# The following cases are special cases
print("I love %s"%100)
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I love you
I love 100
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s = "I am d years old."
print(s%19)
The following print will report an error
#print(s%"19")
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I am 19 years oldCopy the code

s = "I am %fKG weight, %fm Heigh"
print(s)

If more than one message needs to be formatted, use parentheses
# The following print uses the default format, with many extra zeros
print(s%(60.3.1.76))

The actual amount of information to be formatted must match the amount of data given after the percent sign, otherwise an error is reported
If you want to format the data, you need to format the data
s = "I am %.2fKG weight, %.2fm Heigh"
print(s%(60.3.1.76))
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I am %fKG weight, % FM Heigh I am 60.300000KG weight, 1.760000m Heigh I am 60.30kg weight, 1.76m HeighCopy the code

The format to format

• Use a functional format instead of a percent sign

# cannot specify position, read sequentially
Way # 1
s = "{} {}!"
print(s.format("Hello"."world"))

Way # 2
s = "{} {}!".format("Hello"."World")
print(s)    # is equivalent to printing "Hello World!"

# set the specified position
s = "{0} {1}".format("Hello"."World")
print(s)

# set the specified position
s = "{1} {0}".format("Hello"."World")
print(s)

# set the specified position
s = "I love {0} and {0} loves me".format("you")
print(s)

# The following case reported error, compare with the above case
# s = "I love {} and {} loves me".format("you")
# print(s)

# use named parameters
s = "We are {school_name}, our website is {url}, {teacher} the most handsome"
s = s.format(school_name = "A", url = "B", teacher = "C")
print(s)
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Hello world! Hello World! Hello World Hello I love you and you love meCopy the code

Set parameters by dictionary, unpack
# use named parameters
s = "We are {school_name}, our website is {url}, {teacher} the most handsome"

s_dict = {"school_name":"A", \"url":"B", \"teacher":"C"}
# ** is the unpacking operation
s = s.format(**s_dict)
print(s)
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We are A. Our website is B. C. is the coolestCopy the code

Number formatting is required
s = "A is {:.2f}m heigh, {:.2f}KG weight"
print(s.format(1.84.76.45))

# ^, <, > are centered, left aligned, and right aligned respectively, followed by a width
The character followed by the # : sign can be only one character. If not specified, the character is filled with a space by default
# + displays + before positive numbers and - before negative numbers; (space) Indicates that a space is added before a positive number
# b, d, o, x are binary, decimal, octal, hexadecimal respectively
We can also use curly braces {} to escape curly braces

s = "The format function uses {} for placeholders."
print(s)
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A is 1.84m heigh, 76.45kg weight format uses {} for placeholdersCopy the code

STR built-in function

• Many languages use strings, but Python uses STR to represent strings

help(str)
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Help on class str in module builtins:

class str(object)
 |  str(object='') -> str
 |  str(bytes_or_buffer[, encoding[, errors]]) -> str
 |  
 |  Create a new string object from the given object. If encoding or
 |  errors is specified, then the object must expose a data buffer
 |  that will be decoded using the given encoding and error handler.
 |  Otherwise, returns the result of object.__str__() (if defined)
 |  or repr(object).
 |  encoding defaults to sys.getdefaultencoding().
 |  errors defaults to 'strict'.
 |  
 |  Methods defined here:
 |  
 |  __add__(self, value, /)
 |      Return self+value.
 |  
 |  __contains__(self, key, /)
 |      Return key in self.
 |  
 |  __eq__(self, value, /)
 |      Return self==value.
 |  
 |  __format__(self, format_spec, /)
 |      Return a formatted version of the string as described by format_spec.
 |  
 |  __ge__(self, value, /)
 |      Return self>=value.
 |  
 |  __getattribute__(self, name, /)
 |      Return getattr(self, name).
 |  
 |  __getitem__(self, key, /)
 |      Return self[key].
 |  
 |  __getnewargs__(...)
 |  
 |  __gt__(self, value, /)
 |      Return self>value.
 |  
 |  __hash__(self, /)
 |      Return hash(self).
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __le__(self, value, /)
 |      Return self<=value.
 |  
 |  __len__(self, /)
 |      Return len(self).
 |  
 |  __lt__(self, value, /)
 |      Return self<value.
 |  
 |  __mod__(self, value, /)
 |      Return self%value.
 |  
 |  __mul__(self, value, /)
 |      Return self*value.
 |  
 |  __ne__(self, value, /)
 |      Return self!=value.
 |  
 |  __repr__(self, /)
 |      Return repr(self).
 |  
 |  __rmod__(self, value, /)
 |      Return value%self.
 |  
 |  __rmul__(self, value, /)
 |      Return value*self.
 |  
 |  __sizeof__(self, /)
 |      Return the size of the string in memory, in bytes.
 |  
 |  __str__(self, /)
 |      Return str(self).
 |  
 |  capitalize(self, /)
 |      Return a capitalized version of the string.
 |      
 |      More specifically, make the first character have upper case and the rest lower
 |      case.
 |  
 |  casefold(self, /)
 |      Return a version of the string suitable for caseless comparisons.
 |  
 |  center(self, width, fillchar=' ', /)
 |      Return a centered string of length width.
 |      
 |      Padding is done using the specified fill character (default is a space).
 |  
 |  count(...)
 |      S.count(sub[, start[, end]]) -> int
 |      
 |      Return the number of non-overlapping occurrences of substring sub in
 |      string S[start:end].  Optional arguments start and end are
 |      interpreted as in slice notation.
 |  
 |  encode(self, /, encoding='utf-8', errors='strict')
 |      Encode the string using the codec registered for encoding.
 |      
 |      encoding
 |        The encoding in which to encode the string.
 |      errors
 |        The error handling scheme to use for encoding errors.
 |        The default is 'strict' meaning that encoding errors raise a
 |        UnicodeEncodeError.  Other possible values are 'ignore', 'replace' and
 |        'xmlcharrefreplace' as well as any other name registered with
 |        codecs.register_error that can handle UnicodeEncodeErrors.
 |  
 |  endswith(...)
 |      S.endswith(suffix[, start[, end]]) -> bool
 |      
 |      Return True if S ends with the specified suffix, False otherwise.
 |      With optional start, test S beginning at that position.
 |      With optional end, stop comparing S at that position.
 |      suffix can also be a tuple of strings to try.
 |  
 |  expandtabs(self, /, tabsize=8)
 |      Return a copy where all tab characters are expanded using spaces.
 |      
 |      If tabsize is not given, a tab size of 8 characters is assumed.
 |  
 |  find(...)
 |      S.find(sub[, start[, end]]) -> int
 |      
 |      Return the lowest index in S where substring sub is found,
 |      such that sub is contained within S[start:end].  Optional
 |      arguments start and end are interpreted as in slice notation.
 |      
 |      Return -1 on failure.
 |  
 |  format(...)
 |      S.format(*args, **kwargs) -> str
 |      
 |      Return a formatted version of S, using substitutions from args and kwargs.
 |      The substitutions are identified by braces ('{' and '}').
 |  
 |  format_map(...)
 |      S.format_map(mapping) -> str
 |      
 |      Return a formatted version of S, using substitutions from mapping.
 |      The substitutions are identified by braces ('{' and '}').
 |  
 |  index(...)
 |      S.index(sub[, start[, end]]) -> int
 |      
 |      Return the lowest index in S where substring sub is found, 
 |      such that sub is contained within S[start:end].  Optional
 |      arguments start and end are interpreted as in slice notation.
 |      
 |      Raises ValueError when the substring is not found.
 |  
 |  isalnum(self, /)
 |      Return True if the string is an alpha-numeric string, False otherwise.
 |      
 |      A string is alpha-numeric if all characters in the string are alpha-numeric and
 |      there is at least one character in the string.
 |  
 |  isalpha(self, /)
 |      Return True if the string is an alphabetic string, False otherwise.
 |      
 |      A string is alphabetic if all characters in the string are alphabetic and there
 |      is at least one character in the string.
 |  
 |  isascii(self, /)
 |      Return True if all characters in the string are ASCII, False otherwise.
 |      
 |      ASCII characters have code points in the range U+0000-U+007F.
 |      Empty string is ASCII too.
 |  
 |  isdecimal(self, /)
 |      Return True if the string is a decimal string, False otherwise.
 |      
 |      A string is a decimal string if all characters in the string are decimal and
 |      there is at least one character in the string.
 |  
 |  isdigit(self, /)
 |      Return True if the string is a digit string, False otherwise.
 |      
 |      A string is a digit string if all characters in the string are digits and there
 |      is at least one character in the string.
 |  
 |  isidentifier(self, /)
 |      Return True if the string is a valid Python identifier, False otherwise.
 |      
 |      Use keyword.iskeyword() to test for reserved identifiers such as "def" and
 |      "class".
 |  
 |  islower(self, /)
 |      Return True if the string is a lowercase string, False otherwise.
 |      
 |      A string is lowercase if all cased characters in the string are lowercase and
 |      there is at least one cased character in the string.
 |  
 |  isnumeric(self, /)
 |      Return True if the string is a numeric string, False otherwise.
 |      
 |      A string is numeric if all characters in the string are numeric and there is at
 |      least one character in the string.
 |  
 |  isprintable(self, /)
 |      Return True if the string is printable, False otherwise.
 |      
 |      A string is printable if all of its characters are considered printable in
 |      repr() or if it is empty.
 |  
 |  isspace(self, /)
 |      Return True if the string is a whitespace string, False otherwise.
 |      
 |      A string is whitespace if all characters in the string are whitespace and there
 |      is at least one character in the string.
 |  
 |  istitle(self, /)
 |      Return True if the string is a title-cased string, False otherwise.
 |      
 |      In a title-cased string, upper- and title-case characters may only
 |      follow uncased characters and lowercase characters only cased ones.
 |  
 |  isupper(self, /)
 |      Return True if the string is an uppercase string, False otherwise.
 |      
 |      A string is uppercase if all cased characters in the string are uppercase and
 |      there is at least one cased character in the string.
 |  
 |  join(self, iterable, /)
 |      Concatenate any number of strings.
 |      
 |      The string whose method is called is inserted in between each given string.
 |      The result is returned as a new string.
 |      
 |      Example: '.'.join(['ab', 'pq', 'rs']) -> 'ab.pq.rs'
 |  
 |  ljust(self, width, fillchar=' ', /)
 |      Return a left-justified string of length width.
 |      
 |      Padding is done using the specified fill character (default is a space).
 |  
 |  lower(self, /)
 |      Return a copy of the string converted to lowercase.
 |  
 |  lstrip(self, chars=None, /)
 |      Return a copy of the string with leading whitespace removed.
 |      
 |      If chars is given and not None, remove characters in chars instead.
 |  
 |  partition(self, sep, /)
 |      Partition the string into three parts using the given separator.
 |      
 |      This will search for the separator in the string.  If the separator is found,
 |      returns a 3-tuple containing the part before the separator, the separator
 |      itself, and the part after it.
 |      
 |      If the separator is not found, returns a 3-tuple containing the original string
 |      and two empty strings.
 |  
 |  replace(self, old, new, count=-1, /)
 |      Return a copy with all occurrences of substring old replaced by new.
 |      
 |        count
 |          Maximum number of occurrences to replace.
 |          -1 (the default value) means replace all occurrences.
 |      
 |      If the optional argument count is given, only the first count occurrences are
 |      replaced.
 |  
 |  rfind(...)
 |      S.rfind(sub[, start[, end]]) -> int
 |      
 |      Return the highest index in S where substring sub is found,
 |      such that sub is contained within S[start:end].  Optional
 |      arguments start and end are interpreted as in slice notation.
 |      
 |      Return -1 on failure.
 |  
 |  rindex(...)
 |      S.rindex(sub[, start[, end]]) -> int
 |      
 |      Return the highest index in S where substring sub is found,
 |      such that sub is contained within S[start:end].  Optional
 |      arguments start and end are interpreted as in slice notation.
 |      
 |      Raises ValueError when the substring is not found.
 |  
 |  rjust(self, width, fillchar=' ', /)
 |      Return a right-justified string of length width.
 |      
 |      Padding is done using the specified fill character (default is a space).
 |  
 |  rpartition(self, sep, /)
 |      Partition the string into three parts using the given separator.
 |      
 |      This will search for the separator in the string, starting at the end. If
 |      the separator is found, returns a 3-tuple containing the part before the
 |      separator, the separator itself, and the part after it.
 |      
 |      If the separator is not found, returns a 3-tuple containing two empty strings
 |      and the original string.
 |  
 |  rsplit(self, /, sep=None, maxsplit=-1)
 |      Return a list of the words in the string, using sep as the delimiter string.
 |      
 |        sep
 |          The delimiter according which to split the string.
 |          None (the default value) means split according to any whitespace,
 |          and discard empty strings from the result.
 |        maxsplit
 |          Maximum number of splits to do.
 |          -1 (the default value) means no limit.
 |      
 |      Splits are done starting at the end of the string and working to the front.
 |  
 |  rstrip(self, chars=None, /)
 |      Return a copy of the string with trailing whitespace removed.
 |      
 |      If chars is given and not None, remove characters in chars instead.
 |  
 |  split(self, /, sep=None, maxsplit=-1)
 |      Return a list of the words in the string, using sep as the delimiter string.
 |      
 |      sep
 |        The delimiter according which to split the string.
 |        None (the default value) means split according to any whitespace,
 |        and discard empty strings from the result.
 |      maxsplit
 |        Maximum number of splits to do.
 |        -1 (the default value) means no limit.
 |  
 |  splitlines(self, /, keepends=False)
 |      Return a list of the lines in the string, breaking at line boundaries.
 |      
 |      Line breaks are not included in the resulting list unless keepends is given and
 |      true.
 |  
 |  startswith(...)
 |      S.startswith(prefix[, start[, end]]) -> bool
 |      
 |      Return True if S starts with the specified prefix, False otherwise.
 |      With optional start, test S beginning at that position.
 |      With optional end, stop comparing S at that position.
 |      prefix can also be a tuple of strings to try.
 |  
 |  strip(self, chars=None, /)
 |      Return a copy of the string with leading and trailing whitespace remove.
 |      
 |      If chars is given and not None, remove characters in chars instead.
 |  
 |  swapcase(self, /)
 |      Convert uppercase characters to lowercase and lowercase characters to uppercase.
 |  
 |  title(self, /)
 |      Return a version of the string where each word is titlecased.
 |      
 |      More specifically, words start with uppercased characters and all remaining
 |      cased characters have lower case.
 |  
 |  translate(self, table, /)
 |      Replace each character in the string using the given translation table.
 |      
 |        table
 |          Translation table, which must be a mapping of Unicode ordinals to
 |          Unicode ordinals, strings, or None.
 |      
 |      The table must implement lookup/indexing via __getitem__, for instance a
 |      dictionary or list.  If this operation raises LookupError, the character is
 |      left untouched.  Characters mapped to None are deleted.
 |  
 |  upper(self, /)
 |      Return a copy of the string converted to uppercase.
 |  
 |  zfill(self, width, /)
 |      Pad a numeric string with zeros on the left, to fill a field of the given width.
 |      
 |      The string is never truncated.
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs) from builtins.type
 |      Create and return a new object.  See help(type) for accurate signature.
 |  
 |  maketrans(x, y=None, z=None, /)
 |      Return a translation table usable for str.translate().
 |      
 |      If there is only one argument, it must be a dictionary mapping Unicode
 |      ordinals (integers) or characters to Unicode ordinals, strings or None.
 |      Character keys will be then converted to ordinals.
 |      If there are two arguments, they must be strings of equal length, and
 |      in the resulting dictionary, each character in x will be mapped to the
 |      character at the same position in y. If there is a third argument, it
 |      must be a string, whose characters will be mapped to None in the result.
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