Cheatography
https://cheatography.com
List of useful python features
This is a draft cheat sheet. It is a work in progress and is not finished yet.
Lists
Add or remove |
Append |
my_list.append(element)
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Insert |
my_list.insert(index, element)
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Remove by value |
my_list.remove(element)
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Remove by index |
del my_list[index]
or my_list.pop(index)
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Data Manipulation |
List comprehension |
[expression for item in list if condition]
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Sorting |
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Index of element |
my_list.index(element)
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Count of element |
my_list.count(element)
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Min/Max |
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Concatenation |
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List multiplication |
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Conditional checks |
if all(logic)
or if any(logic)
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Data Conversion |
List to string |
'separator'.join(my_list)
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String to list |
string.split('separator')
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Shallow copy |
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Deep copy (requires import copy) |
copy.deepcopy(my_list)
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Slicing |
Start, end, steps |
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Reverse |
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Negative starts (from end) |
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Useful python
Writing files with open('filename.txt', 'w') as file:
content = file.write()
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Reading files with open('filename.txt', 'r') as file:
content = file.read()
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Checking type if isinstance(x, tuple):
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Tuple unpacking x, y = tuple(1, 2,)
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Timing import time
class Timer:
def __enter__(self): start_time = time.time()
def __exit__(self, *args):end_time = time.time()
print(f"{end_time - start_time} seconds")
with Timer:
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and vs or a = 1 b = 2
print(a or b)
returns a (first true or last false) print(a and b)
returns b (first false or last true) |
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Dictionary (copy)
Add or remove |
Adding/Creating mydict['key'] = mydict['key'].get(v, default) + 1
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Default dict (import defaultdict) defaultdict(default_type)
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Adding/Updating my_dict['key3'] = 'value3'
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Dictionary from two lists dict(zip(list_of_keys, list_of_values))
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Remove del my_dict['key1']
or my_dict.pop('key2')
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Accessing |
Accessing my_dict['key1']
or my_dict.get('key1', 'default_value')
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Keys list list(my_dict.keys())
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Values list list(my_dict.values())
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Key: Value list list(my_dict.items())
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Nested key/values my_dict['outer_key']['inner_key']
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Safer nested dict my_dict.get('outer_key', {}).get('inner_key')
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Filter {k: v for k, v in my_dict.items() if condition}
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Functions |
Iterating for key, value in my_dict.items():
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Looping with enumerate for index, (k, v) in enumerate(my_dict.items()):
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Dict comprehension {k_expr: v_expr for item in iterable}
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Sorting by key dict(sorted(my_dict.items()))
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Sorting by value dict(sorted(my_dict.items(), k=lambda item: item[1]))
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Copying |
Shallow copy new_dict = my_dict.copy()
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Deep copy (import copy) new_dict = copy.deepcopy(my_dict)
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