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Super Kai (Kazuya Ito)
Super Kai (Kazuya Ito)

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String in Python (16)

#python #string #str #function

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*Memos:

format() can format a string as shown below:

*Memos:

  • The 1st or the later arguments are *args(Optional). *Don't use any keyword like *args, args, etc.
  • The 2nd or the later arguments are **kwargs(Optional). *Don't use any keyword like **kwargs, kwargs, etc.

<{} & {index} & {key}>:

*Memos:

  • A {} can output a positional argument with limit. *For example, if there are three positional arguments, three {} can be used as maximum.
  • A {index} can output a positional argument with no limit.
  • A {key} can output a keyword argument with no limit.
  • Both {} and {index} cannot be used at the same time.
  • {} doesn't accept any spaces. 
print('-{}-{}-{}-{k1}-{k2}-'.format('A', 'BC', 'DEF', k1='GH', k2='I'))
print('-{0}-{1}-{2}-{k1}-{k2}-'.format('A', 'BC', 'DEF', k1='GH', k2='I'))
# -A-BC-DEF-GH-I-

print('-{}-{k2}-{}-{k1}-{}-'.format('A', 'BC', 'DEF', k1='GH', k2='I'))
print('-{0}-{k2}-{1}-{k1}-{2}-'.format('A', 'BC', 'DEF', k1='GH', k2='I'))
# -A-I-BC-GH-DEF-

print('-{k2}-{k1}-{2}-{1}-{0}-'.format('A', 'BC', 'DEF', k1='GH', k2='I'))
# -I-GH-DEF-BC-A-

print('-{1}{0}-{k2}{0}{1}-{2}{2}-'.format('A', 'BC', 'DEF', k1='GH', k2='I'))
# -BCA-IABC-DEFDEF-

print(''.format('A', 'BC', 'DEF', k1='GH', k2='I'))
print(''.format())
# Nothing

print('-{}-{}-{}-{}-'.format('A', 'BC', 'DEF', k1='GH', k2='I'))
# IndexError: Replacement index 3 out of range for positional args tuple

print('-{0}-{}-{2}-'.format('A', 'BC', 'DEF', k1='GH', k2='I'))
# ValueError: cannot switch from manual field specification
# to automatic field numbering

print('{ }'.format('ABC'))
# KeyError: ' '

print('{ k }'.format(k='ABC'))
# KeyError: ' k '
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v1 = ['A', 'BC', 'DEF']
v2 = {'k1':'GH', 'k2':'I'}

print('-{}-{}-{}-{k1}-{k2}-'.format(*v1, **v2))
print('-{0}-{1}-{2}-{k1}-{k2}-'.format(*v1, **v2))
# -A-BC-DEF-GH-I-

print('-{}-{k2}-{}-{k1}-{}-'.format(*v1, **v2))
print('-{0}-{k2}-{1}-{k1}-{2}-'.format(*v1, **v2))
# -A-I-BC-GH-DEF-

print('-{k2}-{k1}-{2}-{1}-{0}-'.format(*v1, **v2))
# -I-GH-DEF-BC-A-

print('-{1}{0}-{k2}{0}{1}-{2}{2}-'.format(*v1, **v2))
# -BCA-IABC-DEFDEF-

print(''.format(*v1, **v2))
print(''.format())
# Nothing
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*Format Specification can be used with format() as I explain it with f-strings in my post:

v = -0.0

print('"{:0>-z#010_.0f}"'.format(v))
print('"{:0>-z#10_.0f}"'.format(v))
print('"{:>-z#010_.0f}"'.format(v))
# "000000000."

print('"{0:0>-z#010_.0f}"'.format(v))
print('"{0:0>-z#10_.0f}"'.format(v))
print('"{0:>-z#010_.0f}"'.format(v))
# "000000000."

print('"{:0>-z#010_.0f}" "{:0>-z#10_.0f}" "{:>-z#010_.0f}"'.format(v, v, v))
print('"{0:0>-z#010_.0f}" "{1:0>-z#10_.0f}" "{2:>-z#010_.0f}"'.format(v, v, v))
# "000000000." "000000000." "000000000."
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<index[index] & key[index]>: 

v = ['A', 'B', 'C', 'D']

print('{0}\n- {0[0]} - {0[1]} - {0[2]} - {0[3]}'.format(v))
print('{k}\n- {k[0]} - {k[1]} - {k[2]} - {k[3]}'.format(k=v))
# ['A', 'B', 'C', 'D']
# - A - B - C - D
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v1 = [['A', 'B'], ['C', 'D']]
v2 = '{0}\n- {0[0]} - {0[1]}\n- {0[0][0]} - {0[0][1]} - {0[1][0]} - {0[1][1]}'
v3 = '{k}\n- {k[0]} - {k[1]}\n- {k[0][0]} - {k[0][1]} - {k[1][0]} - {k[1][1]}'

print(v2.format(v1))
print(v3.format(k=v1))
# [['A', 'B'], ['C', 'D']]
# - ['A', 'B'] - ['C', 'D']
# - A - B - C - D
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<index[key] & key[key]>:

*key cannot have "" or ''.

v = {'name':'John', 'age':36}

print('{0}\n- {0[name]} - {0[age]}'.format(v))
print('{k}\n- {k[name]} - {k[age]}'.format(k=v))
# {'name': 'John', 'age': 36}
# - John - 36

print('{0["name"]}'.format(v))
# KeyError: '"name"'

print("{k['age']}".format(k=v))
# KeyError: "'age'"
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v1 = {'person':{'name':'John', 'age':36}}
v2 = '{0}\n- {0[person]}\n- {0[person][name]} - {0[person][age]}'
v3 = '{k}\n- {k[person]}\n- {k[person][name]} - {k[person][age]}'

print(v2.format(v1))
print(v3.format(k=v1))
# {'person': {'name': 'John', 'age': 36}}
# - {'name': 'John', 'age': 36}
#  - John - 36
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<index.key & key.key>:

*key cannot be called with ().

import math

print('{0.pi} - {k.pi}'.format(math, k=math))
# 3.141592653589793 - 3.141592653589793

print('{0.pow}'.format(math))
print('{k.pow}'.format(k=math))
# <built-in function pow>

print('{0.pow(3, 2)}'.format(math))
print('{k.pow(3, 2)}'.format(k=math))
# AttributeError: module 'math' has no attribute 'pow(3, 2)'
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<!s & !r & !a>:

*Memos:

  • !s is str() which can create a string.
  • !r is repr() which can create a printable string.
  • !a is ascii() which can create the printable string of ASCII characters. *Non-ASCII characters are represented with \x, \u, or \U escape. 
v = "Jφhи\tSмiтh"

print("{!s}".format(v))
print("{0!s}".format(v))
print("{k!s}".format(k=v))
# Jφhи    Sмiтh

print("{!r}".format(v))
print("{0!r}".format(v))
print("{k!r}".format(k=v))
# 'Jφhи\tSмiтh'

print("{!a}".format(v))
print("{0!a}".format(v))
print("{k!a}".format(k=v))
# 'J\u03c6h\u0438\tS\u043ci\u0442h'
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v = 'I\'m Jφhи\tSмiтh.'

print('{!s}'.format(v))
print('{0!s}'.format(v))
print('{k!s}'.format(k=v))
# I'm Jφhи    Sмiтh.

print('{!r}'.format(v))
print('{0!r}'.format(v))
print('{k!r}'.format(k=v))
# "I'm Jφhи\tSмiтh."

print('{!a}'.format(v))
print('{0!a}'.format(v))
print('{k!a}'.format(k=v))
# "I'm J\u03c6h\u0438\tS\u043ci\u0442h."
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<{{ & }}>

*Memos:

  • { can escape {.
  • } can escape }. 
print('The bracket {{ is escaped.'.format())
# The bracket { is escaped.

print('The bracket }} is escaped.'.format())
# The bracket } is escaped.

print('The {{brackets}} are escaped.'.format())
# The {brackets} are escaped.
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