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# String format

## format

* 문자열을 가지고 있는 함수 
* "{}".format(10) 형식이며 
* 중괄호의 개수와 괄호안의 매개변수의 개수가 반드시 같아야한다

  ```python
  String_a = "{}".format(10)
  String_b = "{} {}".format(10, 20)
  String_c = "{} {} {}".format(10, 20, 30)  
  print(String_a) # 10
  print(String_b) # 10 20 
  print(String_c) # 10 20 30
  ```

## 문자열 포맷 코드

| 코드 | 설명                   |
| -- | -------------------- |
| %s | 문자열(String)          |
| %c | 문자 1개(Character)     |
| %d | 정수(Integer)          |
| %f | 부동소수(floating-point) |
| %o | 8진수                  |
| %x | 16진수                 |
| %% | Literal % (문자 % 자체)  |

## 포맷 코드 사용

```python
>>> "I eat %s apples." % "five"
'I eat five apples.'
```

```python
>>> "I eat %d apples." % 3
'I eat 3 apples.'
```

```python
>>> number = 3
>>> "I eat %d apples." % number
'I eat 3 apples.'
```

```python
>>> number = 10
>>> day = "three"
>>> "I ate %d apples. so I was sick for %s days." % (number, day)
'I ate 10 apples. so I was sick for three days.'
```

* 정렬과 공백 

  ```python
  >>> "%10s" % "hi"
  '        hi'
  ```

  ```python
  >>> "%-10sjane." % 'hi'
  'hi        jane.'
  ```

  ```python
  >>> "%0.4f" % 3.42134234
  '3.4213'
  ```

  ```python
  >>> "%10.4f" % 3.42134234
  '    3.4213'
  ```

## format 함수를 사용 : "{}".format(x)

* 숫자 대입

  ```python
  >>> "I eat {0} apples".format(3) 
  # {0}은 인덱스로 format 함수의 0번째 값으로 입력하고 출력한다 
  'I eat 3 apples'
  ```
* 문자열 대입

  ```python
  "{0} coffee".format("five")
  'five coffee'
  ```
* 2개상의 값 넣기

  ```python
  >>> "I ate {number} apples. so I was sick for {day} days.".format(number=10, day=3)
  'I ate 10 apples. so I was sick for 3 days.'
  ```
* 소수점 표현하기

  ```python
  >>> y = 3.42134234
  >>> "{0:0.4f}".format(y)
  '3.4213'
  >>> "{0:10.4f}".format(y)
  '    3.4213'
  ```
* { 또는 } 문자 표현하기

  ```python
  >>> "{{ and }}".format()
  '{ and }'
  ```

## format 함수의 정렬과 공백

* 왼쪽 정렬 (:<)

  ```python
  >>> "{0:<10}".format("hi")
  'hi        '
  ```
* 오른쪽 정렬 (:>)

  ```python
  >>> "{0:>10}".format("hi")
  '        hi'
  ```
* 가운데 정렬 (:^)

  ```python
  >>> "{0:^10}".format("hi")
  '    hi    '
  ```
* 정렬 후 공백채우기

  ```python
  >>> "{0:=^10}".format("hi")
  '====hi===='
  >>> "{0:!<10}".format("hi")
  'hi!!!!!!!!'
  ```

## format 함수와 슬라이싱 이용

* format() 함수의 다양한 기능

  ```python
  output_a = "{:d}".format(52)     #52
  ```
* 특정 칸에 출력

  ```python
  output_b = "{:5d}".format(52)    #   52
  output_c = "{:10d}".format(52)   #        52
  ```
* 빈칸을 0으로 채우기

  ```python
  output_d = "{:05d}".format(52)   #00052
  output_e = "{:05d}".format(-52)  #-0052
  ```
* 기호와 함께 출력하기

  ```python
  output_f = "{:+d}".format(52)    #+52 
  output_g = "{:+d}".format(-52)   #-52 
  output_h = "{: d}".format(52)    # 52 # 공백이 채워지지 않는다  
  output_i = "{: d}".format(-52)   #-52
  ```
* 조합하기

  ```python
  output_j = "{:+5d}".format(52)   #  +52 
  output_k = "{:+5d}".format(-52)  #  -52
  output_l = "{:=+5d}".format(52)  #+  52
  output_m = "{:=-5d}".format(-52) #-  52 
  output_n = "{:+05d}".format(52)  #+0052
  output_o = "{:-05d}".format(-52) #-0052
  ```
* 부동 소수점 출력의 다양한 형태

  ```python
  output_1 = "{:f}".format(52.273) #52.273000 # 정수와 유사하다 
  output_2 = "{:15.3f}".format(52.273) # ... 52.273
  output_3 = "{:15.2f}".format(52.273) # ...  52.27
  output_4 = "{:15.1f}".format(52.273) # ...   52.2
  ```
* 의미 없는 부동 소수점 제거

  ```python
  output_g1 = 52.0
  output_g2 = "{:g}".format(output_g1)
  print(output_g1) # 52.0 
  print(output_g2) # 52
  ```


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