常用内置函数（Built-In Functions,BIF）不需要导入任何模块即可直接使用，在IDLE中执行如下命令可以列出所有内置函数和内置对象，如代码块1.3.2.1所示：
1 >>> dir(__builtins__) 2 ['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BlockingIOError', 'BrokenPipeError', 'BufferError',
'BytesWarning', 'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError', 'ConnectionRefusedError', 'ConnectionResetError',
'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FileExistsError', 'FileNotFoundError',
'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError',
'InterruptedError', 'IsADirectoryError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'None',
'NotADirectoryError', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning',
'PermissionError', 'ProcessLookupError', 'RecursionError', 'ReferenceError', 'ResourceWarning', 'RuntimeError', 'RuntimeWarning',
'StopAsyncIteration', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'TimeoutError', 'True',
'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning',
'UserWarning', 'ValueError', 'Warning', 'WindowsError', 'ZeroDivisionError', '__build_class__', '__debug__', '__doc__', '__import__',
'__loader__', '__name__', '__package__', '__spec__', 'abs', 'all', 'any', 'ascii', 'bin', 'bool', 'bytearray', 'bytes',
'callable', 'chr', 'classmethod', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod',
'enumerate', 'eval', 'exec', 'exit', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr',
'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'map',
'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'repr',
'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'vars', 'zip'] 3 >>>
代码块1.3.2.1
可以使用 help(函数名) 查看某个函数的用法，不需要导入模块就可以直接使用 help(模块名)查看该模块的帮助文档，例如 help('math')。help()函数示例，参考代码块1.3.2.2
1 >>> help(abs) 2 Help on built-in function abs in module builtins: 3 4 abs(x, /) 5 Return the absolute value of the argument. 6 7 >>> 8 >>> 9 >>> help(math) 10 Traceback (most recent call last): 11 File "<pyshell#8>", line 1, in <module> 12 help(math) 13 NameError: name 'math' is not defined 14 >>> 15 >>> help('math') 16 Help on built-in module math: 17 18 NAME 19 math 20 21 DESCRIPTION 22 This module is always available. It provides access to the 23 mathematical functions defined by the C standard. 24 25 FUNCTIONS 26 acos(...) 27 acos(x) 28 29 Return the arc cosine (measured in radians) of x. 30 31 acosh(...) 32 acosh(x) 33 34 Return the inverse hyperbolic cosine of x. 35 36 asin(...) 37 asin(x) 38 39 Return the arc sine (measured in radians) of x. 40 41 asinh(...) 42 asinh(x) 43 44 Return the inverse hyperbolic sine of x. 45 46 atan(...) 47 atan(x) 48 49 Return the arc tangent (measured in radians) of x. 50 51 atan2(...) 52 atan2(y, x) 53 54 Return the arc tangent (measured in radians) of y/x. 55 Unlike atan(y/x), the signs of both x and y are considered. 56 57 atanh(...) 58 atanh(x) 59 60 Return the inverse hyperbolic tangent of x. 61 62 ceil(...) 63 ceil(x) 64 65 Return the ceiling of x as an Integral. 66 This is the smallest integer >= x. 67 68 copysign(...) 69 copysign(x, y) 70 71 Return a float with the magnitude (absolute value) of x but the sign 72 of y. On platforms that support signed zeros, copysign(1.0, -0.0) 73 returns -1.0. 74 75 cos(...) 76 cos(x) 77 78 Return the cosine of x (measured in radians). 79 80 cosh(...) 81 cosh(x) 82 83 Return the hyperbolic cosine of x. 84 85 degrees(...) 86 degrees(x) 87 88 Convert angle x from radians to degrees. 89 90 erf(...) 91 erf(x) 92 93 Error function at x. 94 95 erfc(...) 96 erfc(x) 97 98 Complementary error function at x. 99 100 exp(...) 101 exp(x) 102 103 Return e raised to the power of x. 104 105 expm1(...) 106 expm1(x) 107 108 Return exp(x)-1. 109 This function avoids the loss of precision involved in the direct evaluation of exp(x)-1 for small x. 110 111 fabs(...) 112 fabs(x) 113 114 Return the absolute value of the float x. 115 116 factorial(...) 117 factorial(x) -> Integral 118 119 Find x!. Raise a ValueError if x is negative or non-integral. 120 121 floor(...) 122 floor(x) 123 124 Return the floor of x as an Integral. 125 This is the largest integer <= x. 126 127 fmod(...) 128 fmod(x, y) 129 130 Return fmod(x, y), according to platform C. x % y may differ. 131 132 frexp(...) 133 frexp(x) 134 135 Return the mantissa and exponent of x, as pair (m, e). 136 m is a float and e is an int, such that x = m * 2.**e. 137 If x is 0, m and e are both 0. Else 0.5 <= abs(m) < 1.0. 138 139 fsum(...) 140 fsum(iterable) 141 142 Return an accurate floating point sum of values in the iterable. 143 Assumes IEEE-754 floating point arithmetic. 144 145 gamma(...) 146 gamma(x) 147 148 Gamma function at x. 149 150 gcd(...) 151 gcd(x, y) -> int 152 greatest common divisor of x and y 153 154 hypot(...) 155 hypot(x, y) 156 157 Return the Euclidean distance, sqrt(x*x + y*y). 158 159 isclose(...) 160 isclose(a, b, *, rel_tol=1e-09, abs_tol=0.0) -> bool 161 162 Determine whether two floating point numbers are close in value. 163 164 rel_tol 165 maximum difference for being considered "close", relative to the 166 magnitude of the input values 167 abs_tol 168 maximum difference for being considered "close", regardless of the 169 magnitude of the input values 170 171 Return True if a is close in value to b, and False otherwise. 172 173 For the values to be considered close, the difference between them 174 must be smaller than at least one of the tolerances. 175 176 -inf, inf and NaN behave similarly to the IEEE 754 Standard. That 177 is, NaN is not close to anything, even itself. inf and -inf are 178 only close to themselves. 179 180 isfinite(...) 181 isfinite(x) -> bool 182 183 Return True if x is neither an infinity nor a NaN, and False otherwise. 184 185 isinf(...) 186 isinf(x) -> bool 187 188 Return True if x is a positive or negative infinity, and False otherwise. 189 190 isnan(...) 191 isnan(x) -> bool 192 193 Return True if x is a NaN (not a number), and False otherwise. 194 195 ldexp(...) 196 ldexp(x, i) 197 198 Return x * (2**i). 199 200 lgamma(...) 201 lgamma(x) 202 203 Natural logarithm of absolute value of Gamma function at x. 204 205 log(...) 206 log(x[, base]) 207 208 Return the logarithm of x to the given base. 209 If the base not specified, returns the natural logarithm (base e) of x. 210 211 log10(...) 212 log10(x) 213 214 Return the base 10 logarithm of x. 215 216 log1p(...) 217 log1p(x) 218 219 Return the natural logarithm of 1+x (base e). 220 The result is computed in a way which is accurate for x near zero. 221 222 log2(...) 223 log2(x) 224 225 Return the base 2 logarithm of x. 226 227 modf(...) 228 modf(x) 229 230 Return the fractional and integer parts of x. Both results carry the sign 231 of x and are floats. 232 233 pow(...) 234 pow(x, y) 235 236 Return x**y (x to the power of y). 237 238 radians(...) 239 radians(x) 240 241 Convert angle x from degrees to radians. 242 243 sin(...) 244 sin(x) 245 246 Return the sine of x (measured in radians). 247 248 sinh(...) 249 sinh(x) 250 251 Return the hyperbolic sine of x. 252 253 sqrt(...) 254 sqrt(x) 255 256 Return the square root of x. 257 258 tan(...) 259 tan(x) 260 261 Return the tangent of x (measured in radians). 262 263 tanh(...) 264 tanh(x) 265 266 Return the hyperbolic tangent of x. 267 268 trunc(...) 269 trunc(x:Real) -> Integral 270 271 Truncates x to the nearest Integral toward 0. Uses the __trunc__ magic method. 272 273 DATA 274 e = 2.718281828459045 275 inf = inf 276 nan = nan 277 pi = 3.141592653589793 278 279 FILE 280 (built-in) 281 282 283 >>>
常用内置函数及其功能简要说明如表1.3.2.3所示，其中方括号内的参数可以忽略
| 函数 | 功能简要说明 |
| abs(x) | 返回数字 x 的绝对值或复数的模 |
| all(iterable) | 如果对于可迭代对象iterable中所有元素 x 都有 bool(x) 为 True，则返回 True。对于空的可迭代对象也返回 True |
| any(iterable) | 只要可迭代iterable中存在元素x使得bool(x)为True，则返回True。对于空的可迭代对象返回False |
| bin(x) | 将数字x转换为二进制 |
| bool(x) | 返回与x等价的布尔值 True 或 False |
| callable(object) | 测试对象object是否可调用，类和函数是可调用的，包含__call__()方法的类的对象也是可调用的 |
| compile() | 用于把Python代码编译成可被 exec() 或 eval() 函数执行的代码对象 |
| chr(x) | 返回Unicode编码为x的字符 |
| dir(obj) | 返回指定对象obj或模块obj的成员列表 |
| eval(s[,globals[,locals]]) | 计算并返回字符串 s 中表达式的值 |
| exec(x) | 执行代码或代码对象 x |
| filter(func,seq) | 返回filter对象，其中包含序列seq中使得单参数函数func返回值为True的那些元素，如果函数func为None则返回那些值等价于True的元素 |
| float(x) | 把数字或字符串x转换为浮点数并返回 |
| hasattr(obj,name) | 测试对象obj是否具有成员name |
| hash(x) | 返回对象 x 的哈希值，如果 x 不可哈希则抛出异常 |
| help(obj) | 返回对象obj的帮助信息 |
| hex(x) | 把数字x转换为十六进制 |
| id(obj) | 返回对象obj的帮助信息 |
| input([提示内容字符串]) | 接收键盘输入的内容，返回字符串 |
| int(x[,d]) | 返回数字x的整数部分，或把d进制的字符串转换为十进制并返回，d默认为十进制 |
| isinstance(object,class-or-type-or-tuple) | 测试对象object是否属于指定类型（如果有多个类型的话需要放到tuple中）的实例 |
| len(obj) | 返回对象obj包含的元素个数，适用于列表、元组、集合、字典、字符串、range对象和其他可迭代类型的对象 |
| list([x])、set([x])、tuple([x])、dict([x]) | 把对象x转换为列表、集合、元组、或字典并返回，或生成空列表、空集合、空元组、空字典 |
| map(func,seq) | 将函数func映射至序列seq中每个元素，返回包含函数值的map对象 |
| max(x)、min(x) | 返回序列x中的最大值、最小值，要求序列x中的所有元素之间可比较大小 |
| next(x) | 返回可迭代对象x中的下一个元素 |
| sum(x) | 返回序列x中所有元素之和，要求序列x中的所有元素必须为数字 |
| oct(x) | 把数字x转换为八进制 |
| open(name[,mode]) | 以指定模式mode打开文件name并返回文件对象 |
| ord(x) | 返回一个字符x的Unicode编码 |
| pow(x,y) | 返回x的y次方，等价于x **y |
|
print(value,...,sep='',end=' ',file= sys.stdout,flush=False) |
基本输出函数 |
| range([start,]end[,step]) | 返回range对象，其中包含(start,end)区间以步长的整数 |
| reduce(func,seq) | 将双参数的函数func以迭代的方式从左到右依次应用至序列seq中每个元素，最终返回单个值作为结果。在Python3版本中需要从functools模块中导入reduce函数再使用 |
| reversed(seq) | 返回seq（可以是列表、元组、字符串、range以及其他可迭代对象）中所有元素逆序后的迭代器对象 |
| round(x[,小数位数]) | 对x进行四舍五入，若不指定小数位数，则返回整数 |
| str(obj) | 把对象obj直接转换为字符串 |
|
sorted(iterbale,key=None, reverse=False) |
返回排序后的列表，其中iterable表示要排序的序列或迭代对象，key用来指定排序规则或依据，reverser用来指定升序或降序。该函数不改变iterable内任何元素的顺序 |
| type(obj) | 返回对象obj的类型 |
| zip(seq1[,seq2[...]]) | 返回zip对象，其中元素为(seqi[i],seq2[i],...)形式的元组 |
小提示：
（1）：可以通过内置函数help()查看某个函数的使用帮助；
（2）：编写程序时应优先考虑使用内置函数，因为内置函数不仅程序、稳定，而且速度相对较快；
（3）：可以导入sys模块后使用print(sys.builtin_module_names)查看Python所有内置模块名称；
1 >>> import sys
2 >>>
3 >>> print(sys.builtin_module_names)
4 ('_ast', '_bisect', '_codecs', '_codecs_cn', '_codecs_hk', '_codecs_iso2022', '_codecs_jp', '_codecs_kr', '_codecs_tw', '_collections', '_csv', '_datetime', '_functools', '_heapq', '_imp', '_io', '_json', '_locale', '_lsprof', '_md5', '_multibytecodec', '_opcode', '_operator', '_pickle', '_random', '_sha1', '_sha256', '_sha512', '_signal', '_sre', '_stat', '_string', '_struct', '_symtable', '_thread', '_tracemalloc', '_warnings', '_weakref', '_winapi', 'array', 'atexit', 'audioop', 'binascii', 'builtins', 'cmath', 'errno', 'faulthandler', 'gc', 'itertools', 'marshal', 'math', 'mmap', 'msvcrt', 'nt', 'parser', 'sys', 'time', 'winreg', 'xxsubtype', 'zipimport', 'zlib')
5 >>>
（4）：可以使用help('modules')查看本机所有可用模块名称。
help('modules')
1 >>> help('modules') 2 3 Please wait a moment while I gather a list of all available modules... 4 5 AutoComplete _pydecimal ensurepip pydoc 6 AutoCompleteWindow _pyio enum pydoc_data 7 AutoExpand _random errno pyexpat 8 Bindings _sha1 faulthandler queue 9 CallTipWindow _sha256 filecmp quopri 10 CallTips _sha512 fileinput random 11 ClassBrowser _signal fnmatch re 12 CodeContext _sitebuiltins formatter reprlib 13 ColorDelegator _socket fractions rlcompleter 14 Debugger _sqlite3 ftplib rpc 15 Delegator _sre functools run 16 EditorWindow _ssl gc runpy 17 FileList _stat genericpath sched 18 FormatParagraph _string getopt select 19 GrepDialog _strptime getpass selectors 20 HyperParser _struct gettext setuptools 21 IOBinding _symtable glob shelve 22 IdleHistory _testbuffer gzip shlex 23 MultiCall _testcapi hashlib shutil 24 MultiStatusBar _testimportmultiple heapq signal 25 ObjectBrowser _testmultiphase help site 26 OutputWindow _thread hmac smtpd 27 ParenMatch _threading_local html smtplib 28 PathBrowser _tkinter http sndhdr 29 Percolator _tracemalloc idle socket 30 PyParse _warnings idle_test socketserver 31 PyShell _weakref idlelib sqlite3 32 RemoteDebugger _weakrefset idlever sre_compile 33 RemoteObjectBrowser _winapi imaplib sre_constants 34 ReplaceDialog abc imghdr sre_parse 35 RstripExtension aboutDialog imp ssl 36 ScriptBinding aifc importlib stat 37 ScrolledList antigravity inspect statistics 38 SearchDialog argparse io string 39 SearchDialogBase array ipaddress stringprep 40 SearchEngine ast itertools struct 41 StackViewer asynchat json subprocess 42 ToolTip asyncio keybindingDialog sunau 43 TreeWidget asyncore keyword symbol 44 UndoDelegator atexit lib2to3 symtable 45 WidgetRedirector audioop linecache sys 46 WindowList base64 locale sysconfig 47 ZoomHeight bdb logging tabbedpages 48 __future__ binascii lzma tabnanny 49 __main__ binhex macosxSupport tarfile 50 _ast bisect macpath telnetlib 51 _bisect builtins macurl2path tempfile 52 _bootlocale bz2 mailbox test 53 _bz2 cProfile mailcap textView 54 _codecs calendar marshal textwrap 55 _codecs_cn cgi math this 56 _codecs_hk cgitb mimetypes threading 57 _codecs_iso2022 chunk mmap time 58 _codecs_jp cmath modulefinder timeit 59 _codecs_kr cmd msilib tkinter 60 _codecs_tw code msvcrt token 61 _collections codecs multiprocessing tokenize 62 _collections_abc codeop netrc trace 63 _compat_pickle collections nntplib traceback 64 _compression colorsys nt tracemalloc 65 _csv compileall ntpath tty 66 _ctypes concurrent nturl2path turtle 67 _ctypes_test configDialog numbers turtledemo 68 _datetime configHandler opcode types 69 _decimal configHelpSourceEdit operator typing 70 _dummy_thread configSectionNameDialog optparse unicodedata 71 _elementtree configparser os unittest 72 _functools contextlib parser urllib 73 _hashlib copy pathlib uu 74 _heapq copyreg pdb uuid 75 _imp crypt pickle venv 76 _io csv pickletools warnings 77 _json ctypes pip wave 78 _locale curses pipes weakref 79 _lsprof datetime pkg_resources webbrowser 80 _lzma dbm pkgutil winreg 81 _markupbase decimal platform winsound 82 _md5 difflib plistlib wsgiref 83 _msi dis poplib xdrlib 84 _multibytecodec distutils posixpath xml 85 _multiprocessing doctest pprint xmlrpc 86 _opcode dummy_threading profile xxsubtype 87 _operator dynOptionMenuWidget pstats zipapp 88 _osx_support easy_install pty zipfile 89 _overlapped email py_compile zipimport 90 _pickle encodings pyclbr zlib 91 92 Enter any module name to get more help. Or, type "modules spam" to search 93 for modules whose name or summary contain the string "spam". 94 95 >>>
本节练习代码如下：要听董老师的，不要眼高手低，一定要动手练习，遇到不懂的可以自己百度一下。
1 =========================abs(x)
2 >>> abs(-3) #返回数字的绝对值
3 3
4 >>>
5 >>> abs(3 + 5j) #返回复数的模
6 5.830951894845301
7 >>>
8
9 =========================all(iterable)
10 >>> all('12306') #字符串是可迭代对象，'12306'的所有元素 x 都有 bool(x) 为 True，故返回 True
11 True
12 >>> bool('0')
13 True
14 >>>
15 >>> all(['',None]) #列表也是可迭代对象，但其中的元素''和None 的bool结果都是False，所以all() 返回False
16 False
17 >>>
18 >>> bool('')
19 False
20 >>> bool(None)
21 False
22 >>>
23 >>> all('') #空的可迭代对象也返回True
24 True
25 >>>
26
27 =========================any(iterable)
28 >>> any(['',None,1]) #虽然bool('')、bool(None)为False，单bool(1)为True ，故any()返回True
29 True
30 >>>
31 >>> any('') #空的可迭代对象返回False
32 False
33 >>>
34
35 =========================bin(x)
36 >>> bin(2) #看来bin()的参数只能是正负整数，不能是浮点数
37 '0b10'
38 >>> bin(-2)
39 '-0b10'
40 >>> bin(2.1)
41 Traceback (most recent call last):
42 File "<pyshell#55>", line 1, in <module>
43 bin(2.1)
44 TypeError: 'float' object cannot be interpreted as an integer
45 >>>
46
47 =========================bool(x)
48 >>> bool(1)
49 True
50 >>> bool(1.1)
51 True
52 >>> bool(-1)
53 True
54 >>> bool(1 + j)
55 Traceback (most recent call last):
56 File "<pyshell#64>", line 1, in <module>
57 bool(1 + j)
58 NameError: name 'j' is not defined
59 >>>
60 >>> bool(0)
61 False
62 >>>
63 >>> bool('s')
64 True
65 >>> bool('')
66 False
67
68 总结：bool()函数返回False的三种情况：数值0、空的可迭代对象、None，其他对象返回True。
69
70 =========================callable(object)
71 >>> def myfun():
72 pass
73
74 >>>
75 >>> class Mycls():
76 pass
77
78 >>>
79 >>> m = Mycls()
80 >>>
81 >>> callable(myfun)
82 True
83 >>> callable(Mycls)
84 True
85 >>> callable(m) #因为m对象没有__callable__()方法，故返回False
86 False
87 >>>
88 >>> m.__call__():
89
90 SyntaxError: invalid syntax
91 >>> m.__call__()
92 Traceback (most recent call last):
93 File "<pyshell#111>", line 1, in <module>
94 m.__call__()
95 AttributeError: 'Mycls' object has no attribute '__call__'
96 >>>
97
98 =========================compile()
99 >>> s = "print('hello world')"
100 >>> ss = compile(s,'','single')
101 >>> ss
102 <code object <module> at 0x00000000034E1660, file "", line 1>
103 >>>
104 >>> exec(ss)
105 hello world
106
107
108 格式：compile( str, file, type )
109
110 compile语句是从type类型（包括’eval’: 配合eval使用，’single’: 配合单一语句的exec使用，’exec’: 配合多语句的exec使用）中将str里面的语句创建成代码对象。
111 file是代码存放的地方，通常为”。
112
113 拓展一篇文章：
114 标题：Python可执行对象——exec、eval、compile
115 URL：http://www.pythoner.com/56.html
116
117
118 =========================chr()
119 >>> chr(11) #参数一定要是正整数，
120 'x0b'
121 >>>
122 >>>
123 >>> chr(97)
124 'a'
125 >>>
126 >>> chr(200)
127 'è'
128 >>>
129
130
131 =========================dir(obj)
132 #根据说明，obj可以是Python的对象也可以是模块
133 >>> class Student():
134 def __init__(self,name):
135 self.name = name
136
137 >>>
138 >>> dir(Student) #Student是Python的对象
139 ['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__']
140 >>>
141 >>>
142 >>> dir('math') #math是模块
143 ['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']
144 >>>
145
146
147 =========================eval(s[,globals[,locals]])
148 >>> d = {'ph':1}
149 >>> eval('ph + 3',d)
150 4
151 >>>
152
153
154 拓展URL：https://www.cnblogs.com/sesshoumaru/p/5995712.html
155
156
157 =========================exec(x)
158 exec函数和eval函数类似，也是执行动态语句，只不过eval函数只用于执行表达式求值，而exec函数主要用于执行语句块。
159
160 >>> s = 'a = 1 + 1'
161 >>> exec(s)
162 >>> a
163 2
164
165 拓展URL:https://www.cnblogs.com/sesshoumaru/p/5998523.html
166
167
168 =========================filter(func,seq)
169 #filter有两个参数,func为函数，seq为序列
170 >>> def func(x):
171 return x % 2 ==0
172
173 >>>
174 >>> seq = range(0,20)
175 >>>
176 >>>
177 >>> f = filter(func,seq) #注意第一个参数为函数名，表示的是func这个对象，func()的话会限制性函数，将函数返回值作为filter()的第一个参数，这点要切记
178 >>> list(f)
179 [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
180 >>>
181
182
183 =========================float(x)
184 >>> float(2)
185 2.0
186 >>>
187 >>> float('1')
188 1.0
189 >>> float('1.0')
190 1.0
191 >>>
192
193
194 =========================hasattr(obj,name)
195 >>> class Student():
196 def __init__(self,name,age):
197 self.name = name
198 self.age = age
199
200
201 >>>
202 >>> hasattr(Student,'name')
203 False
204 >>>
205 >>> s = Student('zhangsan',10)
206 >>> hasattr(s,'name')
207 True #说明这个name属性是属于Student的具体的对象的，而非类的，当然类也可有自己的属性，给Student再加一个属性看看
208 >>>
209 >>> class Student():
210 count = 0
211 def __init__(self,name,age):
212 self.name = name
213 self.age = age
214
215
216 >>> hasattr(Student,'count')
217 True
218 >>>
219 >>> s = Student('lisi','20')
220 >>> hasattr(s,'count') #看来类的属性，也属于其子类。我们可以用这个类属性count统计一共实例化了多少次
221 True
222 >>>
223
224
225 #Student每实例化一次，count的值就会加1
226 >>> class Student():
227 count = 0
228 def __init__(self,name,age):
229 self.name = name
230 self.age = age
231 Student.count += 1
232
233
234 >>>
235 >>> s1 = Student('11',11)
236 >>> s2 = Student('22',22)
237 >>>
238 >>> s2.count
239 2
240 >>> s1.count
241 2
242 >>> Student.count
243 2
244
245
246 =========================hex(x)
247 >>> a = 33
248 >>> hex(a)
249 '0x21'
250 >>>
251
252
253 =========================input([提示内容字符串])
254 >>> a = input('请输入您的年龄
')
255 请输入您的年龄
256 18
257 >>> a
258 '18'
259 >>> int(a)
260 18
261 >>> float(a)
262 18.0
263 >>>
264 >>> #虽然input返回的是字符串，但是我们能对字符串进行处理啊
265
266
267 =========================int(x[,d])
268 >>> b = '33'
269 >>> b1 = int(b)
270 >>> b1
271 33
272 >>>
273 >>> #假设b是六进制的，转换为十进制的方法
274 >>>
275 >>> b2 = int(b,6)
276 >>> b2
277 21
278 >>>
279
280 =========================isinstance(object,class-or-type-or-tuple)
281 >>> isinstance(2,int)
282 True
283 >>> isinstance(s,Student)
284 False
285 >>>
286 >>> isinstance('2',(int,float,str))
287 True
288 >>>
289
290
291
292 =========================map(func,seq)
293 #演示一个将字符串'123.456'转换成数字123.456
294
295 from functools import reduce
296
297 def str2num(s):
298 d = {'0':0,'1':1,'2':2,'3':3,'4':4,'5':5,'6':6,'7':7,'8':8,'9':9,'.':'.'}
299 return d[s]
300
301 def get_num(x,y):
302 return x*10 + y
303
304 def changestr(mys):
305
306 l=[]
307 if '.' in mys:
308 l = mys.split('.')
309 else:
310 l.append(mys)
311
312 print('ll:{}'.format(l))
313
314 if len(l) == 1:
315 ll = map(str2num,l[0])
316 num = reduce(get_num,ll)
317 return num
318
319 elif len(l) == 2:
320 ll = []
321 for i in l:
322 li = map(str2num,i)
323 ll += li
324 num = reduce(get_num, ll)
325 cf = len(mys) - mys.index('.') - 1
326 return num / 10 ** cf
327
328 else:
329 print('空字符串还处理啥呢，结束吧')
330
331
332 if __name__ == '__main__':
333 mys = '123.456'
334 print(changestr(mys))
335
336 #执行结果：123.456
337
338 #我在网上找的别人的实现过程，代码就简短的多了，看着真舒服
339 from functools import reduce
340 from math import pow
341 def char2num(s):
342 digits = {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9}
343 return digits[s]
344
345 def str2float(s):
346 l = len(s.split('.')[1])
347 s = s.replace('.','')
348 return reduce(lambda x,y:10*x+y,map(char2num,s))/pow(10,l)
349
350
351 =========================range([start,]end[,step])
352 >>> range(0,5)
353 range(0, 5)
354 >>>
355 >>>
356 >>> range(5) #start参数的默认值为0
357 range(0, 5)
358 >>>
359 >>> range(0,100,10)
360 range(0, 100, 10)
361 >>>
362 >>> list(range(0,100,10))
363 [0, 10, 20, 30, 40, 50, 60, 70, 80, 90]
364 >>>
365
366
367 =========================reversed(seq)
368 >>> l = list(range(0,10))
369 >>> l
370 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
371 >>>
372 >>> ll = list(reversed(l)) #因为是返回的迭代器对象，可以将其转换为list，当然也可以转换为tuple，
373 >>> ll
374 [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
375 >>>
376 >>> l
377 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] #说明经过reversed()函数的转换，是不影响原序列的元素顺序的哦
378
379
380
381 =========================round(x[,小数位数])
382 >>> a = 1
383 >>> b = 1.4
384 >>> c = 1.5
385 >>>
386 >>> round(1)
387 1
388 >>> round(b)
389 1
390 >>> round(c)
391 2
392 >>>
393
394
395
396 =========================sorted(iterbale,key=None,reverse=False)
397 #sorted() 函数的关键应该是key，，以什么规则进行排序
398
399 有一组学成的名字和成绩如下：
400 L = [('Bob', 75), ('Adam', 92), ('Bart', 66), ('Lisa', 88)]
401
402 任务一：请用sorted()对上述列表分别按名字排序：
403
404 L = [('Bob', 75), ('Adam', 92), ('Bart', 66), ('Lisa', 88)]
405
406 def by_name(x):
407 return x[0]
408
409 L2 = sorted(L, key=by_name)
410
411 print(L2)
412
413 #执行结果：[('Adam', 92), ('Bart', 66), ('Bob', 75), ('Lisa', 88)]
414
415
416 任务二：按成绩从高到低排序：
417 我的代码：
418
419 def to_num(x):
420 return x[1]
421
422 lll = sorted(L,key=to_num,reverse=True)
423 print(lll) #[('Adam', 92), ('Lisa', 88), ('Bob', 75), ('Bart', 66)]
424
425
426 #结合着两个例子，可以看出，key是要定义一个函数，如何处理第一个参数中的元素，这个是制定排序标准，自定义按什么排序。
427
428
429
430 =========================zip(seq1[,seq2[...]])
431
432 a1 = [1,2,3]
433 a2 = [4,5,6,7]
434 a3 = [7,8,9]
435 a4 = ["a","b","c","d"]
436
437 zip1=zip(a1,a2,a3,a4)
438
439 for z in zip1:
440 print(z)
441
442 #执行结果如下：
443 (1, 4, 7, 'a')
444 (2, 5, 8, 'b')
445 (3, 6, 9, 'c')
446
447 #观察结果可以发现，zip1中的元素个数是zip()中序列中元素最少的那个序列的元素个数决定。
448
449
450 =========================max(x)
451 #max()函数还有一个key参数，可以指定比较大小的一句，比如：
452 max(['2','111'],key=len)
453 返回值为'111'
454 这个key的值为函数名，我们可以自定义函数来决定以什么样的方式对序列中元素如何比较大小