Create common_ds.md

tech-summary/language/python/common_ds.md

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+# Frequent be used data structures of python
+
+## Basic structure
+
+### str
+
+Built-in data structure, can be used directly without importing
+
+```python
+format(*args, **kwargs)  # Various usage, the algorithm can be used in the string form of the binary conversion
+split(sep=None, maxsplit=-1) 
+strip([chars])
+join(iterable)
+replace(old, new[, count])
+count(substring[, start[, end]])
+startswith(prefix[, start[, end]])
+endswith(suffix[, start[, end]])
+```
+
+spliting/slice
+
+```python
+myString="PythonForBeginners"
+x=myString[0:10:2]  # PtoFr
+x=myString[0:10:3]  # PhFB
+
+txt = "apple#banana#cherry#orange"
+x = txt.split("#", 2)          #  ['apple', 'banana', 'cherry#orange']
+
+```
+
+### tuple
+
++ The only functions provided are index and count
++ Tuples are often used for multivariable assignment and multivalued return, but they are usually used without parentheses to make python look good.
++ It also supports stitching, slicing, repetition and other operations.
++ Use `namedtuple` for lightweight, immutable data containers before you need the flexibility of a full class
+  + You can’t specify default argument values for namedtuple classes. -> dataclass
+  + The attribute values of namedtuple instances are still accessible using numerical indexes and iteration
+
+```python
+from collections import namedtuple
+Grade = namedtuple('Grade', ('score', 'weight'))
+
+
+def __init__(self):
+  self._grades = []
+
+def report_grade(self, score, weight):
+  self._grades.append(Grade(score, weight))
+```
+
+### list
+
+```python
+lst.sort(*, key=None, reverse=False)
+lst.append(val)  # It can also be lst = lst + [val]
+lst.clear()
+lst.count(val)
+lst.extend(t)  # or s += t  # += Actually, the _iadd_ method is called.
+lst.pop(val=lst[-1])
+lst.remove(val)
+lst.reverse() # this changes orginal list
+lst.insert(i, val)
+```
+
+`iteration`
+
+```python
+for index, item in enumerate(items):
+    print(index, "-->", item)
+```
+
+`append` vs `extend`
++ `Append` means to append a data to the bottom of the list as a new element. Its parameters can be any object
++ The parameter of `extend` must be an iterative object, which means that all elements in the object are appended to the back of the list one by one
+
+```python
+x = [1, 2, 3]
+y = [4, 5]
+
+x.append(y) # x: [1, 2, 3, [4, 5]]
+# reset
+x.extend(y) # [1, 2, 3, 4, 5]
+```
+Check is list empty
+```python
+if not items:
+    Print ("empty list")
+```
+
+
+
+
+
+
+
+## Reference
++ [The 10 most common list operations in Python](https://developpaper.com/the-10-most-common-list-operations-in-python/)
++ Effective python
+