374 lines
10 KiB
HTML
374 lines
10 KiB
HTML
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This is <a href="."><em>Devhints.io cheatsheets</em></a> — a collection of cheatsheets I've written.
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<div class='post-headline -cheatsheet'>
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<p class='prelude'><span></span></p>
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<h1><span>Python</span></h1>
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<div class='post-content -cheatsheet'>
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<h3 id="tuples-immutable">Tuples (immutable)</h3>
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<pre><code>tuple = ()
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</code></pre>
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<h3 id="lists-mutable">Lists (mutable)</h3>
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<pre><code>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 # expands all elements in place
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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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</code></pre>
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<h3 id="dict">Dict</h3>
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<pre><code>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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**dict # expands all k/v pairs in place
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</code></pre>
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<h3 id="iteration">Iteration</h3>
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<pre><code>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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</code></pre>
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<h3 id="string"><a href="https://docs.python.org/2/library/stdtypes.html#string-methods">String</a></h3>
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<pre><code>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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f"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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/* escape characters */
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>>> 'doesn\'t' # use \' to escape the single quote...
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"doesn't"
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>>> "doesn't" # ...or use double quotes instead
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"doesn't"
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>>> '"Yes," they said.'
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'"Yes," they said.'
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>>> "\"Yes,\" they said."
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'"Yes," they said.'
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>>> '"Isn\'t," they said.'
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'"Isn\'t," they said.'
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</code></pre>
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<h3 id="casting">Casting</h3>
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<pre><code>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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</code></pre>
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<h3 id="comprehensions">Comprehensions</h3>
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<pre><code>[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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</code></pre>
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<h3 id="regex">Regex</h3>
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<pre><code>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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</code></pre>
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<h2 id="file-manipulation">File manipulation</h2>
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<h3 id="reading">Reading</h3>
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<pre><code class="language-py">file = open("hello.txt", "r") # open in read mode 'r'
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file.close()
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</code></pre>
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<pre><code class="language-py">print(file.read()) # read the entire file and set the cursor at the end of file
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print file.readline() # Reading one line
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file.seek(0, 0) # place the cursor at the beginning of the file
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</code></pre>
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<h3 id="writing-overwrite">Writing (overwrite)</h3>
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<pre><code class="language-py">file = open("hello.txt", "w") # open in write mode 'w'
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file.write("Hello World")
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text_lines = ["First line", "Second line", "Last line"]
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file.writelines(text_lines)
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file.close()
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</code></pre>
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<h3 id="writing-append">Writing (append)</h3>
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<pre><code class="language-py">file = open("Hello.txt", "a") # open in append mode
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file.write("Hello World again")
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file.close()
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</code></pre>
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<h3 id="context-manager">Context manager</h3>
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<pre><code class="language-py">with open("welcome.txt", "r") as file:
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# 'file' refers directly to "welcome.txt"
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data = file.read()
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# It closes the file automatically at the end of scope, no need for `file.close()`.
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</code></pre>
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<div class="about-the-site">
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<div class="container">
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<p class='blurb'>
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<strong><a href=".">Devhints.io cheatsheets</a></strong> is a collection of cheatsheets I've written over the years.
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Suggestions and corrections? <a href='https://github.com/rstacruz/cheatsheets/issues/907'>Send them in</a>.
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<i class='fleuron'></i>
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I'm <a href="http://ricostacruz.com">Rico Sta. Cruz</a>.
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Check out my <a href="http://ricostacruz.com/til">Today I learned blog</a> for more.
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