python的快速参考手册

Jan 19, 2017

本手册来自图书《Introduction to Computation adn Programming Using Python》。

Common operations on numerical types

i+j is the sum of i and j
i-j is i minus j
i*j is the product（） of i and j
i//jis integer division
i/j is i divided by j. In Python 2.7, when i and j are both of type int, the result is also an int, otherwise the result is a float
i%j is the remainder（余数） when the int i is divided by the int j
i**j is i raised to the power j
x += y is equivalent to x = x + y. *= and -= work the same way

Comparison and Boolean operators

x == y returns True if x and y are equal
x != y returns True if x and y are not equal
<, >, <=, >= have their usual meanings
a and b is True if both a and b are True, and False otherwise
a or b is Ture if at least one of a and b is True, and False otherwise
not a is True if a is Fasle, and False if a if True

Common operations on sequence types

seq[i] returns the ith element in the sequence
len(seq) returns the length of the sequence
seq1 + seq2 concatenates（链接） the two sequences
n*seq returns a sequence that repeats seq n times
seq[start:end] returns a slice（切片） of the sequence
e in seq tests whether e is contained in the sequence
e not in seq tests whether e is not contained in the sequence
for e in seq iterates（迭代） over the elements of the sequence

Common string methods

s.count(s1) counts how many times the string s1 occurs in s
s.find(s1) returns the index of the first occurrence of the substring s1 in s; -1 if s1 is not in s
s.rfind(s1) same as find, but starts fron the end of s
s.index(s1) same as find, but raises an exception if s1 is not in s
s.rindx(s1) same as index, but starts from the end of s
s.lower() converts all uppercase letters to lowercase
s.replace(old, new) replaces all occurrences of string old with string new
s.rstrip() removes trailling white space
s.split(d) Splits s using d as a delimiter（分隔符）. Return a list of substrings of s

Common list methos

L.append(e) add the object（对象） e to the end of L
L.count(e) returns the number of times that e occurs in L
L.insert(i, e) inserts the object e into L at index i
L.extend(L1) appends（追加） the items in list L1 to the end of L
L.remove(e) deletes the first occurrence of e from L
L.index(e) returns the index of the first occurrence of e in L
L.pop(i) removes and returns the item at index i. Defaults to -1
L.sort() has the side effect of sorting the elements of L
L.reverse() has the side effect of reversing the order of the elements in L

Common operations on dictionaries

len(d) returns the number of items in d
d.keys() returns a list containing the keys in d
d.values() returns a list containing the values in d
k in d returns True if key k is in d
d[k] returns the item in d with key k. Raises KeyError if k is not in d
d.get(k, v) returns d[k] if k in d, and v otherwise
d[k] = v associates the value v with the key k. If there is already a value associated with k, that value is replaced.
del d[k] removes element with key k from d. Raises KeyError if k is not in d.
for k in d iterates over the keys in d

Comparison of common non-scalar types（non-scalar: have internal structure that can be accessed)

Type	Type of Index	Type f element	Examples of literals	Mutable（可变的）
str	int	characters	’’, ‘a’, ‘abc’	No
tuple	int	any type	(), (3,), (‘abc’, 4)	No
list	int	any type	[], [3], [‘abc’, 4]	Yes
dict	Hashable objects	any type	{}, {‘a’: 1}, {‘a’:1, ‘b’:2.0}	Yes

Common input/output mechanisms

raw_input(msg) prints msg and then returns value entered as a string
print s1, ..., sn prints strings s1, …, sn with a space between each
open('fileName', 'w') creates a file for writing
open('fileName', 'r') opens an existing file for reading
open('fileName', 'a') opens an existing file for appending
fileHandle.read() returns a string containing contents of the file
fileHandle.readline() returns the next line in the file
fileHandle.readlines() returns a list containing lines of the file
fileHandle.write(s) write the string s to the end of the file
fileHandle.writelines(L) Writes each element of L to the file
fileHandle.close() closes the file