Python 2.7快速参考：初学者必备语法与模块指南

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本资源是一份详尽的Python 2.7语法参考指南，特别针对初学者设计，旨在提供清晰的教程和实用的指导。它分为多个部分，包括但不限于： 1. **前言**：介绍了版本2.7的更新内容，以及用户可以访问官方更新信息的网址，并鼓励报告任何发现的问题、不准确之处和改进建议，以便与作者Richard Gruet保持联系。 2. **调用选项**：这部分可能涉及如何正确地启动和配置Python解释器，包括环境变量设置。 3. **词法实体**：详细解释了Python的关键字、标识符、字符串常量、布尔值、数字类型、序列（如列表）、字典、集合、运算符等基础概念。 4. **基本类型和操作**：涵盖了Python的None、布尔值、数值类型（整型、浮点型等）、序列处理、文件操作、集合、命名元组、日期/时间等核心概念及操作方法。 5. **高级类型**：介绍了迭代器、生成器、描述符、装饰器等进阶主题，这些都是实现更复杂程序结构的重要工具。 6. **语句与控制流程**：涵盖赋值、条件表达式、控制流（if-else、循环等）、异常处理以及函数和类定义的语法和用法。 7. **内置函数和异常**：列出了Python内置的函数库，如sys、os、time等，以及如何处理常见的错误和异常。 8. **用户自定义类中的标准方法与重写**：讲解如何在用户创建的类中覆盖或扩展内置操作。 9. **特殊信息状态属性**：介绍了一些数据类型特有的状态属性，有助于深入理解Python内部机制。 10. **重要模块**：列举了标准库中的一些关键模块，如re（正则表达式）、math（数学计算）、os（操作系统接口）等，以及它们在实际开发中的应用。 11. **工作区探索与编程习惯提示**：提供了如何有效利用工作空间资源以及遵循Python编程的最佳实践建议。 12. **Emacs下的Python模式**：如果读者使用Emacs编辑器，这部分将介绍如何设置Python特定的环境和快捷键。最后，整个文档遵循Creative Commons许可协议，允许用户在规定范围内自由分享和使用。这份参考文档是学习和掌握Python 2.7语法的良好起点，无论是初学者还是进阶开发者都能从中获益良多。

• (4) The pop() method is not supported by mutable sequence types other than lists. The optional argument i defaults

to -1, so that by default the last item is removed and returned.

• (5) Raises a TypeError when x is not a list object.

• (6) append vs. extend: append takes any object and places as last element in list, while extend only takes a iterable

object and extends the list with each element in x.

Op eratio n s on mapp i ngs / dictionari es (type d i c t )

Operations on mappings

Operation Result Notes

len(d) The number of items in d

dict()

dict(**kwargs)

dict(iterable)

dict(d)

Creates an empty dictionary.

Creates a dictionary init with the keyword args kwargs.

Creates a dictionary init with (key, value) pairs provided by iterable.

Creates a dictionary which is a copy of dictionary d.

d.fromkeys(iterable, value=None) Class method to create a dictionary with keys provided by iterator, and

all values set to value.

d[k] The item of d with key k (1)

d[k] = x Set d[k] to x

del d[k] Removes d[k] from d (1)

d.clear() Removes all items from d

d.copy() A shallow copy of d

d.has_key(k)

k in d

True if d has key k, else False

d.items() A copy of d's list of (key, item) pairs (2)

d.keys() A copy of d's list of keys (2)

d1.update(d2)

for k, v in d2.items(): d1[k] = v

Since 2.4, update(**kwargs) and update(iterable) may also be used.

d.values() A copy of d's list of values (2)

d.get(k [, defaultval]) The item of d with key k (3)

d.setdefault(k[,defaultval]) d[k] if k in d, else defaultval (and inserts it) (4)

d.iteritems() Returns an iterator over (key, value) pairs.

d.iterkeys() Returns an iterator over the mapping's keys.

d.itervalues() Returns an iterator over the mapping's values.

d.pop(k[, default]) Removes key k and returns the corresponding value. If key is not found,

default is returned if given, otherwise KeyError is raised.

d.popitem() Removes and returns an arbitrary (key, value) pair from d

d.viewitems() Returns a view object of the (key, value) pairs (5)

d.viewkeys() Returns a view object of the mappings keys (5)

d.viewvalues() Returns a view object of the mappings values (5)

Notes:

• TypeError is raised if key is not acceptable.

• (1) KeyError is raised if key k is not in the map.

• (2) Keys and values are listed in random order.

• (3) Never raises an exception if k is not in the map, instead it returns defaultval. defaultval is optional, when not

provided and k is not in the map, None is returned.

• (4) Never raises an exception if k is not in the map, instead returns defaultVal, and adds k to map with value

defaultVal. defaultVal is optional. When not provided and k is not in the map, None is returned and added to map.

• (5) A view object provides a dynamic view on the dictionary's entries, which means that when the dictionary

changes, the view reflects these changes. A view object is also iterable.

Op eratio n s on stri ngs (types s t r & u n i c o d e )

These string methods largely (but not completely) supersede the functions available in the string module.

The str and unicode types share a common base class basestring.

Operations on strings

Operation Result Notes

s.capitalize() Returns a copy of s with its first character capitalized, and the rest of the

characters lowercased.

s.center(width[, fillChar=' ']) Returns a copy of s centered in a string of length width, surrounded by the

appropriate number of fillChar characters.

(1)

s.count(sub[, start[, end]]) Returns the number of occurrences of substring sub in string s. (2)

s.decode([encoding[, errors]]) Returns a unicode string representing the decoded version of str s, using the

given codec (encoding). Useful when reading from a file or a I/O function that

handles only str. Inverse of encode.

(3)

s.encode([encoding[, errors]]) Returns a str representing an encoded version of s. Mostly used to encode a

unicode string to a str in order to print it or write it to a file (since these I/O

functions only accept str), e.g. u'légère'.encode('utf8'). Also used to

encode a str to a str, e.g. to zip (codec 'zip') or uuencode (codec 'uu') it. Inverse

of decode.

(3)

s.endswith(suffix [, start[, end]]) Returns True if s ends with the specified suffix, otherwise return false. Since 2.5

suffix can also be a tuple of strings to try.

(2)

s.expandtabs([tabsize]) Returns a copy of s where all tab characters are expanded using spaces. (4)

s.find(sub [,start[,end]]) Returns the lowest index in s where substring sub is found. Returns -1 if sub is

not found.

(2)

s.format(*args, *kwargs)

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Operation Result Notes

Returns s after replacing numeric and named formatting references found in

braces {}. (details)

s.index(sub[, start[, end]]) like find(), but raises ValueError when the substring is not found. (2)

s.isalnum() Returns True if all characters in s are alphanumeric, False otherwise. (5)

s.isalpha() Returns True if all characters in s are alphabetic, False otherwise. (5)

s.isdigit() Returns True if all characters in s are digit characters, False otherwise. (5)

s.islower() Returns True if all characters in s are lowercase, False otherwise. (6)

s.isspace() Returns True if all characters in s are whitespace characters, False otherwise. (5)

s.istitle() Returns True if string s is a titlecased string, False otherwise. (7)

s.isupper() Returns True if all characters in s are uppercase, False otherwise. (6)

separator.join(seq) Returns a concatenation of the strings in the sequence seq, separated by string

separator, e.g.: ",".join(['A', 'B', 'C']) -> "A,B,C"

s.ljust/rjust/center(width[,

fillChar=' '])

Returns s left/right justified/centered in a string of length width. (1), (8)

s.lower() Returns a copy of s converted to lowercase.

s.lstrip([chars] ) Returns a copy of s with leading chars (default: blank chars) removed.

s.partition(separ) Searches for the separator separ in s, and returns a tuple (head, sep, tail)

containing the part before it, the separator itself, and the part after it. If the

separator is not found, returns (s, '', '').

s.replace(old, new[, maxCount =-

1])

Returns a copy of s with the first maxCount (-1: unlimited) occurrences of

substring old replaced by new.

(9)

s.rfind(sub[ , start[, end]]) Returns the highest index in s where substring sub is found. Returns -1 if sub

is not found.

(2)

s.rindex(sub[ , start[, end]]) like rfind(), but raises ValueError when the substring is not found. (2)

s.rpartition(separ) Searches for the separator separ in s, starting at the end of s, and returns a

tuple (head, sep, tail) containing the (left) part before it, the separator

itself, and the (right) part after it. If the separator is not found, returns ('', '', s).

s.rstrip([chars]) Returns a copy of s with trailing chars(default: blank chars) removed, e.g.

aPath.rstrip('/') will remove the trailing '/'from aPath if it exists

s.split([ separator[, maxsplit]]) Returns a list of the words in s, using separator as the delimiter string. (10)

s.rsplit([ separator[, maxsplit]]) Same as split, but splits from the end of the string. (10)

s.splitlines([ keepends]) Returns a list of the lines in s, breaking at line boundaries. (11)

s.startswith(prefix [, start[,

end]])

Returns True if s starts with the specified prefix, otherwise returns False.

Negative numbers may be used for start and end.Since 2.5 prefix can also be a

tuple of strings to try.

(2)

s.strip([chars]) Returns a copy of s with leading and trailing chars(default: blank chars)

removed.

s.swapcase() Returns a copy of s with uppercase characters converted to lowercase and vice

versa.

s.title() Returns a titlecased copy of s, i.e. words start with uppercase characters, all

remaining cased characters are lowercase.

s.translate(table[, deletechars='']) Returns a copy of s mapped through translation table table. Characters from

deletechars are removed from the copy prior to the mapping. Since 2.6 table

may also be None (identity transformation) - useful for using translate to

delete chars only.

(12)

s.upper() Returns a copy of s converted to uppercase.

s.zfill(width) Returns the numeric string left filled with zeros in a string of length width.

Notes:

• (1) Padding is done using spaces or the given character.

• (2) If optional argument start is supplied, substring s[start:] is processed. If optional arguments start and end are

supplied, substring s[start:end] is processed.

• (3) Default encoding is sys.getdefaultencoding(), can be changed via sys.setdefaultencoding(). Optional argument

errors may be given to set a different error handling scheme. The default for errors is 'strict', meaning that

encoding errors raise a ValueError. Other possible values are 'ignore' and 'replace'. See also module codecs.

• (4) If optional argument tabsize is not given, a tab size of 8 characters is assumed.

• (5) Returns False if string s does not contain at least one character.

• (6) Returns False if string s does not contain at least one cased character.

• (7) A titlecased string is a string in which uppercase characters may only follow uncased characters and lowercase

characters only cased ones.

• (8) s is returned if width is less than len(s).

• (9) If the optional argument maxCount is given, only the first maxCount occurrences are replaced.

• (10) If separator is not specified or None, any whitespace string is a separator. If maxsplit is given, at most maxsplit

splits are done.

• (11) Line breaks are not included in the resulting list unless keepends is given and true.

• (12) table must be a string of length 256.

Str i ng f orm att ing wit h the % o per a tor

formatString % args --> evaluates to a string

• formatString mixes normal text with C printf format fields :

%[flag][width][.precision] formatCode

where formatCode is one of c, s, i, d, u, o, x, X, e, E, f, g, G, r, % (see table below).

• The flag characters -, +, blank, # and 0 are understood (see table below).

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