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--- 语法:python3语法速查 [2024/01/03 09:45] – 移除 - 外部编辑 (Unknown date) 127.0.0.1
+++ 语法:python3语法速查 [2024/08/06 09:23] (当前版本) – [4. string] user01
@@ 行 1: / 行 1: @@
+====== python3语法速查 ======
+===== - 技巧文章 =====
+{{indexmenu>:linux:python#1}}
+===== - 数组 list/tuple =====
+python有可变数组和不可变数组
+==== - 不可变数组tuple ====
+创建：   <code>array = ()</code>
+==== - 可变数组list ====
+创建：
+<code>array = []</code>
+=== - 数组添加元素 ===
+添加一个元素到数组末尾：
+<code>array.append(insert_item)</code>
+添加另外一个数组的所有元素到一个数组：
+<code>dest_array.extend(insert_array)</code>
+执行效果：insert_array数组内的元素全部append到dest_array, 最终dest_array的数组元素变多。
+<code python>
+s[i] = x
+item i of s is replaced by x
+s[i:j] = t
+slice of s from i to j is replaced by the contents of the iterable t
+del s[i:j]
+same as s[i:j] = []
+s[i:j:k] = t
+the elements of s[i:j:k] are replaced by those of t
+(1)
+del s[i:j:k]
+removes the elements of s[i:j:k] from the list
+s.append(x)
+appends x to the end of the sequence (same as s[len(s):len(s)] = [x])
+s.clear()
+removes all items from s (same as del s[:])
+(5)
+s.copy()
+creates a shallow copy of s (same as s[:])
+(5)
+s.extend(t) or s += t
+extends s with the contents of t (for the most part the same as s[len(s):len(s)] = t)
+s *= n
+updates s with its contents repeated n times
+(6)
+s.insert(i, x)
+inserts x into s at the index given by i (same as s[i:i] = [x])
+s.pop([i])
+retrieves the item at i and also removes it from s
+(2)
+s.remove(x)
+remove the first item from s where s[i] is equal to x
+(3)
+s.reverse()
+reverses the items of s in place
+(4)
+</code>
+==== - 数组length ====
+<code python>
+tmp_array = [1, 2]
+ret_len = len(tmp_array)
+</code>
+===== - dict字典 =====
+==== - 创建dict ====
+<code python>
+#### 方式1
+>>> a = dict(one=1, two=2, three=3)
+>>> b = {'one': 1, 'two': 2, 'three': 3}
+>>> c = dict(zip(['one', 'two', 'three'], [1, 2, 3]))
+>>> d = dict([('two', 2), ('one', 1), ('three', 3)])
+>>> e = dict({'three': 3, 'one': 1, 'two': 2})
+>>> a == b == c == d == e
+True
+### 方式2
+import collections
+dict = collections.OrderedDict()
+</code>
+==== - functions ====
+<code python>
+list(d)
+Return a list of all the keys used in the dictionary d.
+len(d)
+Return the number of items in the dictionary d.
+d[key]
+Return the item of d with key key. Raises a KeyError if key is not in the map.
+d[key] = value
+Set d[key] to value.
+del d[key]
+Remove d[key] from d. Raises a KeyError if key is not in the map.
+key in d
+Return True if d has a key key, else False.
+key not in d
+Equivalent to not key in d.
+keys()
+Return a new view of the dictionary’s keys. See the documentation of view objects.
+</code>
+==== - 使用举例 ====
+<code python>
+for item in a_dict.keys():
+  print(f'key={item}')
+</code>
+===== - string =====
+<code python>
+class str(object='')
+class str(object=b'', encoding='utf-8', errors='strict')
+Return a string version of object. If object is not provided, returns the empty string.
+</code>
+===== - 文件操作 =====
+==== - 打开文件 ====
+fh = open('file.txt', 'r')
+文件打开类型, r - 只读打开，rb - 只读二进制文件打开， w - 只写文件打开， wb - 只写二进制文件打开, a - 追加写
+=== - 读文件操作 ===
+<code python>
+fh = open('file.txt', 'r')
+for line in fh.readlines():
+    line = line.rstrip() # 去除最右侧换行符
+    print(f'line: {line}')
+fh.close()
+</code>
+=== - 写文件操作 ===
+<code python>
+fh = open('file.txt', 'w', encoding='utf-8')
+fh.write('haha\n')
+fh.write(f'hello\n')
+fh.close()
+</code>
+==== - 关闭文件 ====
+<code python>
+fh = open('file.txt', 'r', encoding='utf-8')
+fh.close()
+</code>
+==== - 其它 ====
+=== - os.path ===
+<code python>
+import os
+os.path.exists(path)
+os.path.isfile(path)
+os.path.isdir(path)
+os.path.islink(path)
+os.path.dirname(path)
+os.path.basename(path)
+os.path.abspath(path)
+os.path.isabs(path)
+</code>
+=== - os ===
+<code python>
+import os
+os.getenv(key, default=None)
+os.putenv(key, value)
+os.unsetenv(key)
+os.chmod(path, mode, *, dir_fd=None, follow_symlinks=True)
+os.chown(path, uid, gid, *, dir_fd=None, follow_symlinks=True)
+os.link(src, dst, *, src_dir_fd=None, dst_dir_fd=None, follow_symlinks=True)
+os.symlink(src, dst, target_is_directory=False, *, dir_fd=None)
+os.remove(path, *, dir_fd=None)
+os.unlink(path, *, dir_fd=None)
+os.rename(src, dst, *, src_dir_fd=None, dst_dir_fd=None)
+os.mkdir(path, mode=0o777, *, dir_fd=None)
+os.rmdir(path, *, dir_fd=None)
+os.listdir(path='.')
+os.chdir(path)
+os.getcwd()
+</code>
+===== - base function =====
+==== - eval() ====
+可以用来支持一些逻辑表达式的计算：
+<code python  [enable_line_numbers="true",highlight_lines_extra="25,26"]>
+#!/usr/bin/python3
+import re
+A = '0xaa'
+B = '0xcc'
+C = '0xf0'
+s_prem = 'A&(B|~C)'
+# re.sub(pattern, repl, string, count=0, flags=0)
+# flags=re.IGNORECASE
+s_new_math = s_prem
+s_new_math = re.sub(r'A', '0xaa', s_new_math)
+s_new_math = re.sub(r'B', '0xcc', s_new_math)
+s_new_math = re.sub(r'C', '0xf0', s_new_math)
+print(f's_new_math = {s_new_math}')
+try:
+    ret = eval(s_new_math)
+    print(f'ret = {hex(ret)}')
+except SyntaxError as e:
+    print(e)
+</code>
+==== - getopt() ====
+C-style parser for command line options
+短argument
+<code python>
+>>> import getopt
+>>> args = '-a -b -cfoo -d bar a1 a2'.split()
+>>> args
+['-a', '-b', '-cfoo', '-d', 'bar', 'a1', 'a2']
+>>> optlist, args = getopt.getopt(args, 'abc:d:')
+>>> optlist
+[('-a', ''), ('-b', ''), ('-c', 'foo'), ('-d', 'bar')]
+>>> args
+['a1', 'a2']
+</code>
+长argument
+<code python>
+>>> s = '--condition=foo --testing --output-file abc.def -x a1 a2'
+>>> args = s.split()
+>>> args
+['--condition=foo', '--testing', '--output-file', 'abc.def', '-x', 'a1', 'a2']
+>>> optlist, args = getopt.getopt(args, 'x', [
+    'condition=', 'output-file=', 'testing'])
+>>> optlist
+[('--condition', 'foo'), ('--testing', ''), ('--output-file', 'abc.def'), ('-x', '')]
+>>> args
+['a1', 'a2']
+</code>
+一个比较接近实用的例子
+<code python>
+import getopt, sys
+def main():
+    try:
+        opts, args = getopt.getopt(sys.argv[1:], "ho:v", ["help", "output="])
+    except getopt.GetoptError as err:
+        # print help information and exit:
+        print(err)  # will print something like "option -a not recognized"
+        usage()
+        sys.exit(2)
+    output = None
+    verbose = False
+    for o, a in opts:
+        if o == "-v":
+            verbose = True
+        elif o in ("-h", "--help"):
+            usage()
+            sys.exit()
+        elif o in ("-o", "--output"):
+            output = a
+        else:
+            assert False, "unhandled option"
+    # ...
+if __name__ == "__main__":
+    main()
+</code>
+==== - enumerate() ====
+enumerate(iterable, start=0)
+Return an enumerate object. iterable must be a sequence, an iterator, or some other object which supports iteration. The __next__() method of the iterator returned by enumerate() returns a tuple containing a count (from start which defaults to 0) and the values obtained from iterating over iterable.
+<code python>
+seasons = ['Spring', 'Summer', 'Fall', 'Winter']
+list(enumerate(seasons))
+[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]
+list(enumerate(seasons, start=1))
+[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]
+</code>
+===== - function =====
+==== - 默认参数 ====
+<code python>
+def my_sum (a, b=1):
+  return a+b
+def my_append (new_item, a_list = None):
+  if a_list == None:
+    a_list = []
+  a_list.append(new_item)
+  return a_list
+</code>
+总结：
+  * 默认值为不可变值（比如上述例子中b=1为常数不变值）时，使用不会有问题。
+  * 普通列表项目默认值为可变值，即为对象、list、dict等，最好默认值输入为None， 在使用的时候显示将其初始化为空对象（比如上述使用的a_list = []），这样在不同位置调用此function函数不会产生相互影响。
+===== - 条件判断 =====
+==== - if ====
+<code python>
+if (a == b) :
+  pass
+elif (a == c) :
+  pass
+else:
+  pass
+if (a == b) or (e == f) :
+  pass
+elif (a == c) not (i == j) :
+  pass
+elif (a == c) and (m == n) :
+  pass
+else:
+  pass
+</code>
+===== - 循环 =====
+==== - for ====
+<code python>
+for i in range(10):
+    print(i)
+    break
+for i in range(1,11):
+    print(i)
+    continue
+</code>
+==== - range用法 ====
+<code python>
+ # range(stop)
+ # range(start, stop[, step])
+>>> list(range(10))
+[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+>>> list(range(1, 11))
+[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+>>> list(range(0, 30, 5))
+[0, 5, 10, 15, 20, 25]
+>>> list(range(0, 10, 3))
+[0, 3, 6, 9]
+>>> list(range(0, -10, -1))
+[0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
+>>> list(range(0))
+[]
+>>> list(range(1, 0))
+[]
+</code>
+==== - while ====
+<code python>
+>>> a=3
+>>> while a > 0:
+...  a = a -1
+...  print(a)
+...
+>>>
+</code>
+===== - 正则表达式 =====
+<code python>
+import re
+# 用上r''的方式，其正则表达式的内容跟perl比较想像
+# 可以从中间搜索
+if re.search(r'(abc|def)', "abc"):
+  print(f' matched!')
+#从头开始匹配搜索
+if re.match(r'(abc|def)', "abc"):
+  print(f' matched!')
+# 不匹配,结果=None
+if re.match(r'a', "dbc") == None:
+  print(f' not matched!')
+</code>
+==== - group ====
+<code python>
+>>> m = re.match(r"(\w+) (\w+)", "Isaac Newton, physicist")
+>>> m.group(0)       # The entire match
+'Isaac Newton'
+>>> m.group(1)       # The first parenthesized subgroup.
+'Isaac'
+>>> m.group(2)       # The second parenthesized subgroup.
+'Newton'
+>>> m.group(1, 2)    # Multiple arguments give us a tuple.
+('Isaac', 'Newton')
+</code>
+===== - python操作json =====
+<code python>
+import collections
+import json
+dict0 = collections.OrderedDict()
+dict1 = collections.OrderedDict()
+dict0['line0'] = 'hha0'
+dict0['line1'] = 'hha1'
+dict0['line2'] = 'hha2'
+dict0['line3'] = dict1
+dict1['a'] = 0
+dict1['b'] = 1
+dict1['c'] = 2
+######################################################
+### conver dict to json string
+s_djs = json.dumps(dict0, indent=2)
+print(f's_djs = {s_djs}')
+### conver json string to dict
+tmp_dict = json.loads(s_djs)
+for key in tmp_dict.keys():
+    print(key)
+######################################################
+### dict dump to json file
+hdl0 = open('w0.json', 'w')
+json.dump(dict0, hdl0, indent=2)
+hdl0.close()
+### load json file to dict
+hdl1 = open('w0.json', 'r')
+tmp_dict = json.load(hdl1)
+hdl1.close()
+print(f'tmp_dict = {tmp_dict}')
+</code>
+运行结果：
+<code>
+s_djs = {
+  "line0": "hha0",
+  "line1": "hha1",
+  "line2": "hha2",
+  "line3": {
+    "a": 0,
+    "b": 1,
+    "c": 2
+  }
+}
+line0
+line1
+line2
+line3
+tmp_dict = {'line0': 'hha0', 'line1': 'hha1', 'line2': 'hha2', 'line3': {'a': 0, 'b': 1, 'c': 2}}
+</code>
+===== - 格式转换或输出 =====
+==== - String Methods ====
+<code python>
+str.lower()   -- 转小写
+str.upper()   -- 转大写
+</code>
+==== - 字符串格式化 ====
+=== - 占位符% ===
+  * https://python-reference.readthedocs.io/en/latest/docs/str/formatting.html
+  * https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting
+<code python>
+name = "Li hua"
+age = 24
+print("Hello "+name+", you are " + str(age) + " years old")
+name = "Li hua"
+age = 24
+print("Hello %s, you are %d years old" % (name, age))
+####　字符串
+'%5s' % 's'    #  左留空，占5个字符宽度
+'%-5s' % 's'    #  右留空，占5个字符宽度
+##### 数值
+'%5d' % 200    #  左留空，占5个字符宽度
+'%-5d' % 200    #  右留空，占5个字符宽度
+</code>
+=== - printf样式 ===
+<code python>
+#### printf样式，  %s, %03d，只不过是直接把变量插在%号后面
+print('%(language)s has %(number)03d quote types.' %
+      {'language': "Python", "number": 2})
+Python has 002 quote types.
+</code>
+=== - python3.6之后 f"" 方法 ===
+在python里面双引号和单引号功能是一样的。
+<code python>
+print(f'名字是：{name}，年龄是：{age}')
+</code>
+==== - print to string ====
+<code python>
+import io
+import re
+output = io.StringIO()
+output.write('First line.\n')
+print('Second line.', file=output)
+# Retrieve file contents -- this will be
+# 'First line.\nSecond line.\n'
+contents = output.getvalue()
+contents = re.sub(r'\n', '', contents, count=0)
+# Close object and discard memory buffer --
+# .getvalue() will now raise an exception.
+output.close()
+print(contents)
+</code>
+==== - str.format() ====
+Accessing arguments by position:
+<code python>
+>>> '{0}, {1}, {2}'.format('a', 'b', 'c')
+'a, b, c'
+>>> '{}, {}, {}'.format('a', 'b', 'c')  # 3.1+ only
+'a, b, c'
+>>> '{2}, {1}, {0}'.format('a', 'b', 'c')
+'c, b, a'
+>>> '{2}, {1}, {0}'.format(*'abc')      # unpacking argument sequence
+'c, b, a'
+>>> '{0}{1}{0}'.format('abra', 'cad')   # arguments' indices can be repeated
+'abracadabra'
+>>> print('{:<8} {:<20} {:<20}'.format(data0, data1, data2))
+</code>
+Accessing arguments by name:
+<code python>
+>>> 'Coordinates: {latitude}, {longitude}'.format(latitude='37.24N', longitude='-115.81W')
+'Coordinates: 37.24N, -115.81W'
+>>> coord = {'latitude': '37.24N', 'longitude': '-115.81W'}
+>>> 'Coordinates: {latitude}, {longitude}'.format(**coord)  # 意思是将dict字典展开
+'Coordinates: 37.24N, -115.81W'
+</code>
+Accessing arguments’ items:
+<code python>
+>>> coord = (3, 5)
+>>> 'X: {0[0]};  Y: {0[1]}'.format(coord)
+'X: 3;  Y: 5'
+</code>
+Aligning the text and specifying a width:
+<code python>
+>>> '{:<30}'.format('left aligned')
+'left aligned                  '
+>>> '{:>30}'.format('right aligned')
+'                 right aligned'
+>>> '{:^30}'.format('centered')
+'           centered           '
+>>> '{:*^30}'.format('centered')  # use '*' as a fill char
+'***********centered***********'
+</code>
+Replacing %x and %o and converting the value to different bases:
+<code python>
+>>> # format also supports binary numbers
+>>> "int: {0:d};  hex: {0:x};  oct: {0:o};  bin: {0:b}".format(42)
+'int: 42;  hex: 2a;  oct: 52;  bin: 101010'
+>>> # with 0x, 0o, or 0b as prefix:
+>>> "int: {0:d};  hex: {0:#x};  oct: {0:#o};  bin: {0:#b}".format(42)
+'int: 42;  hex: 0x2a;  oct: 0o52;  bin: 0b101010'
+</code>
+==== - format数值格式转换 ====
+=== - float保留2位小数 ===
+<code python>
+>>> i = 503
+>>> j = 100
+>>> format(i/j, ".2f")
+'5.03'
+</code>
+=== - 转换为二进制数(字符串) ===
+# Convert an integer number to a binary string prefixed with “0b”.
+<code python>
+>>> bin(3)
+'0b11'
+# 如果不想要0b开头，可以使用format 'b'的方式
+>>> format(14, '#b'), format(14, 'b')
+('0b1110', '1110')
+>>> f'{14:#b}', f'{14:b}'
+('0b1110', '1110')
+</code>