137 lines
3.4 KiB
Markdown
137 lines
3.4 KiB
Markdown
---
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title: Python
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category: Python
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---
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### Lists
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list = []
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list[i:j] # returns list subset
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list[-1] # returns last element
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list[:-1] # returns all but the last element
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list[i] = val
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list[i:j] = otherlist # replace ith to jth-1 elements with otherlist
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del list[i:j]
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list.append(item)
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list.extend(another_list)
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list.insert(index, item)
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list.pop() # returns and removes last element from the list
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list.pop(i) # returns and removes i-th element from the list
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list.remove(i) # removes the first item from the list whose value is i
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list1 + list2 # combine two list
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set(list) # remove duplicate elements from a list
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list.reverse() # reverses the elements of the list in-place
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list.count(item)
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sum(list)
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zip(list1, list2) # returns list of tuples with n-th element of both list1 and list2
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list.sort() # sorts in-place, returns None
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sorted(list) # returns sorted copy of list
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",".join(list) # returns a string with list elements seperated by comma
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### Dict
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dict.keys()
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dict.values()
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"key" in dict # let's say this returns False, then...
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dict["key"] # ...this raises KeyError
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dict.get("key") # ...this returns None
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dict.setdefault("key", 1)
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### Iteration
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for item in ["a", "b", "c"]:
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for i in range(4): # 0 to 3
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for i in range(4, 8): # 4 to 7
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for i in range(1, 9, 2): # 1, 3, 5, 7
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for key, val in dict.items():
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for index, item in enumerate(list):
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### [String](https://docs.python.org/2/library/stdtypes.html#string-methods)
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str[0:4]
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len(str)
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string.replace("-", " ")
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",".join(list)
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"hi {0}".format('j')
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"hi {name}" # same as "hi {}".format('name')
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str.find(",")
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str.index(",") # same, but raises IndexError
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str.count(",")
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str.split(",")
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str.lower()
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str.upper()
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str.title()
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str.lstrip()
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str.rstrip()
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str.strip()
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str.islower()
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### Casting
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int(str)
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float(str)
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str(int)
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str(float)
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'string'.encode()
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### Comprehensions
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[fn(i) for i in list] # .map
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map(fn, list) # .map, returns iterator
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filter(fn, list) # .filter, returns iterator
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[fn(i) for i in list if i > 0] # .filter.map
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### Regex
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import re
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re.match(r'^[aeiou]', str)
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re.sub(r'^[aeiou]', '?', str)
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re.sub(r'(xyz)', r'\1', str)
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expr = re.compile(r'^...$')
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expr.match(...)
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expr.sub(...)
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### File manipulation
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# Reading
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file = open("hello.txt", "r") #open the file in readmode 'r'
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file.close()
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print(file.read()) # read the file
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print fh.readline() # Reading line by line
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# Writing ( Overwrite the previous content ! )
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file = open("hello.txt","w") # open the fil in write mode
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write("Hello World")
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text_lines = ["First line", "Second line", "a third and last line"]
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file.writelines(text_lines) # write the 3 line above inside hello.txt
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file.close()
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# Append File
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file = open("Hello.txt", "a") #open file in append mode
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write("Hello World again")
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file.close()
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# Context Manager
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with open("welcome.txt" ,"r") as file: # file refer directly to the "welcome.txt" , mode = r , w , a
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data = file.read()
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# it close the file automatically no need for file.close()
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