자료구조 : 문자열

문자열 (String)

• 출력 포멧팅
  - end 옵션 값을 이용한 출력
  - %를 사용한 출력
  - {}를 사용한 출력
  - f 문자열 포맷팅

  Ex. end option

  ```
  print("Hello Python", end='')
  print("Hello Python", end='\n') 	# default : end='\n' 
  ```

  ㄴ> 출력 값

  ```
  Hello PythonHello Python
  ```

  Ex. using %

  ```
  # %s(str) / %f(float) / %d(integer) / %c(character)
  # -------------------
  print("Hello! %s" %('James'))
  print("%.3f" %(3.1415))
  print("%d" %(12.5))
  print("%c" %('a'))
  ```

  ㄴ> 출력 값

  ```
  Hello! James
  3.142
  12
  a
  ```

  Ex. using {}

  ```
  print("Welcome to {}".format('파이썬'))
  print("Welcome to {}".format('3.14'))
  print("Welcome to {}".format('12'))
  print("Welcome to {}".format('w'))
  print("Welcome to {} {} {}".format('파이썬', 3.14, '아'))
  print("my favorite movie is {:03d}".format(7))
  print("원주율은 ? {:.2f}".format(3.141592))
  ```

  ㄴ> 출력 값

  ```
  Welcome to 파이썬
  Welcome to 3.14
  Welcome to 12
  Welcome to w
  Welcome to 파이썬 3.14 아
  my favorite movie is 007
  원주율은 ? 3.14
  ```

  Ex. f formating

  ```
  name = John
  age = 15
  PI = 3.141592
  print(f"My name is {name}, and I'm {age}years old.")
  print(f"PI = {PI:.2f}"
  ```    

  ㄴ> 출력 값

  ```
  My name is John, and I'm 15years old.
  PI = 3.14
  ```

• indexing / slicing
  - index order starts at '0'
  - index reverse order starts at '-1'
  

  Ex.

  ```
  my_str = "python"
  # -------------------
  # indexing
  # my_str[0] = p
  # my_str[4] = o
  # my_str[-1] = n
  # -------------------
  # slicing
  # my_str[1:4] = yth
  # my_str[:] = python
  # my_str[2:] = thon
  # my_str[:4] = pyth
  # my_str[-2:] = on
  # my_str[-4:-1] = tho
  # my_str[-4:1] = ' ' space
  # my_str[0:6:2] = pto ; step = 2
  # my_str[::2] = pto ; :: means all, and step = 2
  # my_str[::-1] = nohtyp ; step = -1 means reverse step 1
  ```

• Str functions 1) split, join
  - split() : use it when you want to split the str
  - join() : use it when you want to join the list

  Ex.

  ```
  movies = "미나리, 경계선, 기생충, 학교"
  # ------------------------------------------------
  movieList = movies.split(",")
  # movieList = ['미나리', '경계선', '기생충', '학교']
  # ------------------------------------------------
  movie = ''.join(movieList)
  # movie = "미나리 경계선 기생충 학교"
  ```

• Str functions 2) lower, upper
  - lower() : makes all characters in the string lowercase
  - upper() : makes all characters in the string uppercase

  Ex.

  ```
  a = "This is an apple"
  #
  print(a.lower())	# this is an apple
  print(a.upper()) 	# THIS IS AN APPLE
  ```

• Str functions 3) startswith, endswith
  - startswith("==") : return T / F : if str starts with "=="
  - endswith("==") : return T / F : if str ends with "=="

  Ex.

  ```
  a = "01_star.png"
  #
  print(a.startswith("01"))	# True
  print(a.endswith("png"))	# True
  ```

• Str functions 4) replace
  - replace("==", "--") : replace "==" (in the string) with "--"

  Ex.

  ```
  a = "01_sample.png"
  a = a.replace("png", "mp3")
  # a = "01_sample.mp3"
  ```

• Str functions 5) lstrip, rstrip, strip
  - lstrip() : remove left-side spaces in the string
  - rstrip() : remove right-side spaces in the string
  - strip() : remove both-side spaces in the string

  Ex.

  ```
  a = "     01_sample.png"
  b = "01_sample.png     "
  c = "     01_sample.png     "
  #
  a = a.lstrip()	# a = "01_sample.png"
  b = b.rstrip()	# b = "01_sample.png"
  c = c.strip()	# c = "01_sample.png"
  ```