字串是 Python 中最常用的資料型別。我們可以使用引號('或")來建立字串。
# eg_v1 var1 = "hello,welcome to python~" print (var1) print (type(var1))
注：標準的序列操作（索引,分片,乘法,判斷成員資格,求長度,取最大值和最小值）對字串也是適用的.但字串是不可變的,分片賦值不合法.
1.字串格式化
注：如果需要轉換的元組作為轉換表示式的一部分存在，必須將它用圓括號括起來
格式化符號說明
# 格式化符號 說明 # %c 轉換成字元（ASCII 碼值，或者長度為一的字串） # %r 優先用repr()函式進行字串轉換（Python2.0新增） # %s 優先用str()函式進行字串轉換 # %d / %i 轉成有符號十進位制數 # %u 轉成無符號十進位制數 # %o 轉成無符號八進位制數 # %x / %X (Unsigned)轉成無符號十六進位制數（x / X 代表轉換後的十六進位制字元的大小寫） # %e / %E 轉成科學計數法（e / E控制輸出e / E） # %f / %F 轉成浮點數（小數部分自然截斷） # %g / %G %e和%f / %E和%F 的簡寫 # %% 輸出%
2. 簡單轉換
# eg_v2
print ("price of eggs: $%d" % 42)
print ("Hexadecimal price of eggs: %x" % 42)
3. 欄位寬頻和精度
欄位寬度 是轉換後的值保留最小字元個數
精度 是結果中包含的小數位數
#eg_v3
from math import pi
print ("%10f " % pi) # 字寬度為10
print ("%10.2f" %pi) # 欄位寬 10，精度2
print ("%.2f" % pi) # 精度 2
4. 符號、對齊 和 0 填充
在欄位寬度和精度值之前可以放置一個“標表”，該標表可以為零，加號，減號或空格。零表示數字將會用0填充
字串格式化例項
name = input("input your name:")
age = int(input("input your age:"))
job = input("input your job:")
msg = '''
information of user of %s:
-------------------------
Nane: %s
Age: %d
Job: %s
--------End--------------
''' %(name,name,age,job)
print (msg)
# %s 代表字串格式
# %d 代表整數格式
# %f 代表浮點數格式
字串方法
1. find
find 方法可以在一個較長的字串中查詢子字串。
moo = "with a moo-moo here.and a moo-moo there."
print (moo.find("moo"))
# # 7
tittle = "monty python's flying circus"
print (tittle.find("python"))
# 6
字串操作方法
字串可以使用雙引號或單引號來表示開始和結束，。使用雙引號的一個好處，就是字串中可以使用單引號字元
字串轉義字元
轉義字元 含義 \(在行尾時) 續行符 \\ 反斜槓符號 \' 單引號 \" 雙引號 \a 響鈴 \b 退格(Backspace) \e 轉義 \000 空 \n 換行 \v 縱向製表符 \t 橫向製表符 \r 回車 \f 換頁 \oyy 八進位制數，yy代表的字元，例如：\o12代表換行 \xyy 十六進位制數，yy代表的字元，例如：\x0a代表換行 \other 其它的字元以普通格式輸出
原始字串
在字串開始的引號之前加上r，使它成為原始字串。“原始字串”完全忽略所有的轉義字元，列印出字串中所有的倒斜槓
print (r"hello,welvome to python\n,and\r") # hello,welvome to python\n,and\r
字串下標和切片
字串像列表一樣，使用下標和切片
L = "WelcomeToPython" print (L[0]) print (L[4]) print (L[-1]) print (L[0:5]) print (L[:5]) print (L[6:0]) # W # o # n # Welco # Welco
字串的in 和not in 操作符
像列表一樣，in 和not in 操作符也可以用於字串。用in 或not in 連線兩個字串得到的表示式，將求值為布林值True 或False
L = "Welcome To Python"
print ("To" in L)
print ("And" in L)
print ("Python" not in L)
# True
# False
# False
字串方法upper()、lower()、isupper()和islower()
upper()字串方法返回一個新字串，其中原字串的所有字母都被相應地轉換為大寫
lower()字串方法返回一個新字串，其中原字串的所有字母都被相應地轉換為小寫
L = "Welcome To Python" l1 = L.upper() print (l1) # WELCOME TO PYTHON l2 = L.lower() print (l2) # welcome to python
如果字串至少有一個字母，並且所有字母都是大寫或小寫，isupper()和islower()方法就會相應地返回布林值True。否則，該方法返回False
l3 = l1.isupper() print (l3) # True l4 = l2.islower() print (l4) # True
isX 字串方法
isalpha()返回True，如果字串只包含字母，並且非空； isalnum()返回True，如果字串只包含字母和數字，並且非空； isdecimal()返回True，如果字串只包含數字字元，並且非空； isspace()返回True，如果字串只包含空格、製表符和換行，並且非空； istitle()返回True，如果字串僅包含以大寫字母開頭、後面都是小寫字母的單詞。
字串方法startswith()和endswith()
startswith()和endswith()方法返回True，如果它們所呼叫的字串以該方法傳入的字串開始或結束。否則，方法返回False
print ('Hello world!'.startswith('Hello'))
# True
print ('Hello world!'.endswith('world!'))
# True
字串方法join()和split()
join()方法在一個字串上呼叫，引數是一個字串列表，返回一個字串。返回的字串由傳入的列表中每個字串連線而成
LIST1 = ["A","B","C","D","E","F"]
print ("+".join(LIST1))
# A+B+C+D+E+F
split()用法，是按照換行符分割多行字串
LIST2 = "A+B+C+D+E+F"
print (LIST2.split("+"))
# ['A', 'B', 'C', 'D', 'E', 'F']
用rjust()、ljust()和center()方法對齊文字
rjust()和ljust()字串方法返回撥用它們的字串的填充版本，通過插入空格來對齊文字。這兩個方法的第一個引數是一個整數長度，用於對齊字串
print ("Python".rjust(10)) # 右對齊
# Python
print ("Python".ljust(10)) # 左對齊
# Python
print ("Python".center(10)) # 居中
# Python
用strip()、rstrip()和lstrip()刪除空白字元
刪除字串左邊、右邊或兩邊的空白字元（空格、製表符和換行符）。strip()字串方法將返回一個新的字串，它的開頭或末尾都沒有空白字元。
lstrip()和rstrip()方法將相應刪除左邊或右邊的空白字元。
LIST3 = " Welcome To Python " print (LIST3.strip()) # Welcome To Python print (LIST3.rstrip()) # Welcome To Python print (LIST3.lstrip()) # Welcome To Python
有一個可選的字串引數，指定兩邊的哪些字元應該刪除
LIST4 = "AABBCCDDEEFFAA"
print (LIST4.strip("AA"))
# BBCCDDEEFF
print (LIST4.strip("BB")) # 注：如果不是兩邊的，無法刪除，還是返回原字串
# AABBCCDDEEFFAA
translate，replace
translate 與replace一樣，替換字串的某些部分.但translate只處理單個字元，並且可以同時進行多個替換
字串官方文件解析
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'.
"""
def capitalize(self): # real signature unknown; restored from __doc__
"""
S.capitalize() -> str
Return a capitalized version of S, i.e. make the first character
have upper case and the rest lower case.
"""
return ""
def casefold(self): # real signature unknown; restored from __doc__
"""
S.casefold() -> str
Return a version of S suitable for caseless comparisons.
"""
return ""
def center(self, width, fillchar=None): # real signature unknown; restored from __doc__
"""
S.center(width[, fillchar]) -> str
Return S centered in a string of length width. Padding is
done using the specified fill character (default is a space)
"""
return ""
def count(self, sub, start=None, end=None): # real signature unknown; restored from __doc__
"""
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.
"""
return 0
def encode(self, encoding='utf-8', errors='strict'): # real signature unknown; restored from __doc__
"""
S.encode(encoding='utf-8', errors='strict') -> bytes
Encode S using the codec registered for encoding. Default encoding
is 'utf-8'. errors may be given to set a different error
handling scheme. 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.
"""
return b""
def endswith(self, suffix, start=None, end=None): # real signature unknown; restored from __doc__
"""
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.
"""
return False
def expandtabs(self, tabsize=8): # real signature unknown; restored from __doc__
"""
S.expandtabs(tabsize=8) -> str
Return a copy of S where all tab characters are expanded using spaces.
If tabsize is not given, a tab size of 8 characters is assumed.
"""
return ""
def find(self, sub, start=None, end=None): # real signature unknown; restored from __doc__
"""
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.
"""
return 0
def format(self, *args, **kwargs): # known special case of str.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 '}').
"""
pass
def format_map(self, mapping): # real signature unknown; restored from __doc__
"""
S.format_map(mapping) -> str
Return a formatted version of S, using substitutions from mapping.
The substitutions are identified by braces ('{' and '}').
"""
return ""
def index(self, sub, start=None, end=None): # real signature unknown; restored from __doc__
"""
S.index(sub[, start[, end]]) -> int
Like S.find() but raise ValueError when the substring is not found.
"""
return 0
def isalnum(self): # real signature unknown; restored from __doc__
"""
S.isalnum() -> bool
Return True if all characters in S are alphanumeric
and there is at least one character in S, False otherwise.
"""
return False
def isalpha(self): # real signature unknown; restored from __doc__
"""
S.isalpha() -> bool
Return True if all characters in S are alphabetic
and there is at least one character in S, False otherwise.
"""
return False
def isdecimal(self): # real signature unknown; restored from __doc__
"""
S.isdecimal() -> bool
Return True if there are only decimal characters in S,
False otherwise.
"""
return False
def isdigit(self): # real signature unknown; restored from __doc__
"""
S.isdigit() -> bool
Return True if all characters in S are digits
and there is at least one character in S, False otherwise.
"""
return False
def isidentifier(self): # real signature unknown; restored from __doc__
"""
S.isidentifier() -> bool
Return True if S is a valid identifier according
to the language definition.
Use keyword.iskeyword() to test for reserved identifiers
such as "def" and "class".
"""
return False
def islower(self): # real signature unknown; restored from __doc__
"""
S.islower() -> bool
Return True if all cased characters in S are lowercase and there is
at least one cased character in S, False otherwise.
"""
return False
def isnumeric(self): # real signature unknown; restored from __doc__
"""
S.isnumeric() -> bool
Return True if there are only numeric characters in S,
False otherwise.
"""
return False
def isprintable(self): # real signature unknown; restored from __doc__
"""
S.isprintable() -> bool
Return True if all characters in S are considered
printable in repr() or S is empty, False otherwise.
"""
return False
def isspace(self): # real signature unknown; restored from __doc__
"""
S.isspace() -> bool
Return True if all characters in S are whitespace
and there is at least one character in S, False otherwise.
"""
return False
def istitle(self): # real signature unknown; restored from __doc__
"""
S.istitle() -> bool
Return True if S is a titlecased string and there is at least one
character in S, i.e. upper- and titlecase characters may only
follow uncased characters and lowercase characters only cased ones.
Return False otherwise.
"""
return False
def isupper(self): # real signature unknown; restored from __doc__
"""
S.isupper() -> bool
Return True if all cased characters in S are uppercase and there is
at least one cased character in S, False otherwise.
"""
return False
def join(self, iterable): # real signature unknown; restored from __doc__
"""
S.join(iterable) -> str
Return a string which is the concatenation of the strings in the
iterable. The separator between elements is S.
"""
return ""
def ljust(self, width, fillchar=None): # real signature unknown; restored from __doc__
"""
S.ljust(width[, fillchar]) -> str
Return S left-justified in a Unicode string of length width. Padding is
done using the specified fill character (default is a space).
"""
return ""
def lower(self): # real signature unknown; restored from __doc__
"""
S.lower() -> str
Return a copy of the string S converted to lowercase.
"""
return ""
def lstrip(self, chars=None): # real signature unknown; restored from __doc__
"""
S.lstrip([chars]) -> str
Return a copy of the string S with leading whitespace removed.
If chars is given and not None, remove characters in chars instead.
"""
return ""
def maketrans(self, *args, **kwargs): # real signature unknown
"""
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.
"""
pass
def partition(self, sep): # real signature unknown; restored from __doc__
"""
S.partition(sep) -> (head, sep, tail)
Search for the separator sep in S, and return the part before it,
the separator itself, and the part after it. If the separator is not
found, return S and two empty strings.
"""
pass
def replace(self, old, new, count=None): # real signature unknown; restored from __doc__
"""
S.replace(old, new[, count]) -> str
Return a copy of S with all occurrences of substring
old replaced by new. If the optional argument count is
given, only the first count occurrences are replaced.
"""
return ""
def rfind(self, sub, start=None, end=None): # real signature unknown; restored from __doc__
"""
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.
"""
return 0
def rindex(self, sub, start=None, end=None): # real signature unknown; restored from __doc__
"""
S.rindex(sub[, start[, end]]) -> int
Like S.rfind() but raise ValueError when the substring is not found.
"""
return 0
def rjust(self, width, fillchar=None): # real signature unknown; restored from __doc__
"""
S.rjust(width[, fillchar]) -> str
Return S right-justified in a string of length width. Padding is
done using the specified fill character (default is a space).
"""
return ""
def rpartition(self, sep): # real signature unknown; restored from __doc__
"""
S.rpartition(sep) -> (head, sep, tail)
Search for the separator sep in S, starting at the end of S, and return
the part before it, the separator itself, and the part after it. If the
separator is not found, return two empty strings and S.
"""
pass
def rsplit(self, sep=None, maxsplit=-1): # real signature unknown; restored from __doc__
"""
S.rsplit(sep=None, maxsplit=-1) -> list of strings
Return a list of the words in S, using sep as the
delimiter string, starting at the end of the string and
working to the front. If maxsplit is given, at most maxsplit
splits are done. If sep is not specified, any whitespace string
is a separator.
"""
return []
def rstrip(self, chars=None): # real signature unknown; restored from __doc__
"""
S.rstrip([chars]) -> str
Return a copy of the string S with trailing whitespace removed.
If chars is given and not None, remove characters in chars instead.
"""
return ""
def split(self, sep=None, maxsplit=-1): # real signature unknown; restored from __doc__
"""
S.split(sep=None, maxsplit=-1) -> list of strings
Return a list of the words in S, using sep as the
delimiter string. If maxsplit is given, at most maxsplit
splits are done. If sep is not specified or is None, any
whitespace string is a separator and empty strings are
removed from the result.
"""
return []
def splitlines(self, keepends=None): # real signature unknown; restored from __doc__
"""
S.splitlines([keepends]) -> list of strings
Return a list of the lines in S, breaking at line boundaries.
Line breaks are not included in the resulting list unless keepends
is given and true.
"""
return []
def startswith(self, prefix, start=None, end=None): # real signature unknown; restored from __doc__
"""
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.
"""
return False
def strip(self, chars=None): # real signature unknown; restored from __doc__
"""
S.strip([chars]) -> str
Return a copy of the string S with leading and trailing
whitespace removed.
If chars is given and not None, remove characters in chars instead.
"""
return ""
def swapcase(self): # real signature unknown; restored from __doc__
"""
S.swapcase() -> str
Return a copy of S with uppercase characters converted to lowercase
and vice versa.
"""
return ""
def title(self): # real signature unknown; restored from __doc__
"""
S.title() -> str
Return a titlecased version of S, i.e. words start with title case
characters, all remaining cased characters have lower case.
"""
return ""
def translate(self, table): # real signature unknown; restored from __doc__
"""
S.translate(table) -> str
Return a copy of the string S in which each character has been mapped
through the given translation table. The table must implement
lookup/indexing via __getitem__, for instance a dictionary or list,
mapping Unicode ordinals to Unicode ordinals, strings, or None. If
this operation raises LookupError, the character is left untouched.
Characters mapped to None are deleted.
"""
return ""
def upper(self): # real signature unknown; restored from __doc__
"""
S.upper() -> str
Return a copy of S converted to uppercase.
"""
return ""
def zfill(self, width): # real signature unknown; restored from __doc__
"""
S.zfill(width) -> str
Pad a numeric string S with zeros on the left, to fill a field
of the specified width. The string S is never truncated.
"""
return ""